< draft-ietf-bier-te-arch-11.txt   draft-ietf-bier-te-arch-12.txt >
Network Working Group T.T.E. Eckert, Ed. Network Working Group T.T.E. Eckert, Ed.
Internet-Draft Futurewei Internet-Draft Futurewei
Intended status: Standards Track G.C. Cauchie Intended status: Standards Track M.M. Menth
Expires: 19 May 2022 Bouygues Telecom Expires: 1 August 2022 University of Tuebingen
M.M. Menth G.C. Cauchie
University of Tuebingen Bouygues Telecom
November 2021 January 2022
Tree Engineering for Bit Index Explicit Replication (BIER-TE) Tree Engineering for Bit Index Explicit Replication (BIER-TE)
draft-ietf-bier-te-arch-11 draft-ietf-bier-te-arch-12
Abstract Abstract
This memo describes per-packet stateless strict and loose path This memo describes per-packet stateless strict and loose path
steered replication and forwarding for Bit Index Explicit Replication steered replication and forwarding for "Bit Index Explicit
packets (RFC8279). It is called BIER Tree Engineering (BIER-TE) and Replication" (BIER, RFC8279) packets. It is called BIER Tree
is intended to be used as the path steering mechanism for Traffic Engineering (BIER-TE) and is intended to be used as the path steering
Engineering with BIER. mechanism for Traffic Engineering with BIER.
BIER-TE introduces a new semantic for bit positions (BP) that BIER-TE introduces a new semantic for "bit positions" (BP). They
indicate adjacencies, as opposed to (non-TE) BIER in which BPs indicate adjacencies of the network topology, as opposed to (non-TE)
indicate Bit-Forwarding Egress Routers (BFER). BIER-TE can leverage BIER in which BPs indicate "Bit-Forwarding Egress Routers" (BFER). A
BIER forwarding engines with little changes. Co-existence of BIER BIER-TE packets BitString therefore indicates the edges of the (loop-
and BIER-TE forwarding in the same domain is possible, for example by free) tree that the packet is forwarded across by BIER-TE. BIER-TE
using separate BIER sub-domains (SDs). Except for the optional can leverage BIER forwarding engines with little changes. Co-
routed adjacencies, BIER-TE does not require a BIER routing underlay, existence of BIER and BIER-TE forwarding in the same domain is
and can therefore operate without depending on an Interior Gateway possible, for example by using separate BIER "sub-domains" (SDs).
Routing protocol (IGP). Except for the optional routed adjacencies, BIER-TE does not require
a BIER routing underlay, and can therefore operate without depending
on an "Interior Gateway Routing protocol" (IGP).
As it operates on the same per-packet stateless forwarding As it operates on the same per-packet stateless forwarding
principles, BIER-TE can also be a good fit to support multicast path principles, BIER-TE can also be a good fit to support multicast path
steering in Segment Routing (SR) networks. steering in "Segment Routing" (SR) networks.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Basic Examples . . . . . . . . . . . . . . . . . . . . . 5 2.1. Basic Examples . . . . . . . . . . . . . . . . . . . . . 5
2.2. BIER-TE Topology and adjacencies . . . . . . . . . . . . 8 2.2. BIER-TE Topology and adjacencies . . . . . . . . . . . . 8
2.3. Relationship to BIER . . . . . . . . . . . . . . . . . . 9 2.3. Relationship to BIER . . . . . . . . . . . . . . . . . . 9
2.4. Accelerated/Hardware forwarding comparison . . . . . . . 11 2.4. Accelerated/Hardware forwarding comparison . . . . . . . 11
3. Components . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Components . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. The Multicast Flow Overlay . . . . . . . . . . . . . . . 12 3.1. The Multicast Flow Overlay . . . . . . . . . . . . . . . 12
3.2. The BIER-TE Control Plane . . . . . . . . . . . . . . . . 12 3.2. The BIER-TE Control Plane . . . . . . . . . . . . . . . . 12
3.2.1. The BIER-TE Controller . . . . . . . . . . . . . . . 13 3.2.1. The BIER-TE Controller . . . . . . . . . . . . . . . 14
3.2.1.1. BIER-TE Topology discovery and creation . . . . . 14 3.2.1.1. BIER-TE Topology discovery and creation . . . . . 14
3.2.1.2. Engineered Trees via BitStrings . . . . . . . . . 14 3.2.1.2. Engineered Trees via BitStrings . . . . . . . . . 15
3.2.1.3. Changes in the network topology . . . . . . . . . 15 3.2.1.3. Changes in the network topology . . . . . . . . . 16
3.2.1.4. Link/Node Failures and Recovery . . . . . . . . . 15 3.2.1.4. Link/Node Failures and Recovery . . . . . . . . . 16
3.3. The BIER-TE Forwarding Plane . . . . . . . . . . . . . . 15 3.3. The BIER-TE Forwarding Plane . . . . . . . . . . . . . . 16
3.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 16 3.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 17
3.5. Traffic Engineering Considerations . . . . . . . . . . . 16 3.5. Traffic Engineering Considerations . . . . . . . . . . . 17
4. BIER-TE Forwarding . . . . . . . . . . . . . . . . . . . . . 17 4. BIER-TE Forwarding . . . . . . . . . . . . . . . . . . . . . 18
4.1. The Bit Index Forwarding Table (BIFT) . . . . . . . . . . 17 4.1. The BIER-TE Bit Index Forwarding Table (BIFT) . . . . . . 18
4.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 18 4.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 20
4.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 19 4.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 21
4.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 19 4.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 21
4.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 19 4.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2.4. Local Decap(sulation) . . . . . . . . . . . . . . . . 20 4.2.4. Local Decap(sulation) . . . . . . . . . . . . . . . . 22
4.3. Encapsulation / Co-existence with BIER . . . . . . . . . 20
4.4. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . 21 4.3. Encapsulation / Co-existence with BIER . . . . . . . . . 22
4.5. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 24 4.4. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . 23
4.6. BFR Requirements for BIER-TE forwarding . . . . . . . . . 26 4.5. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 26
5. BIER-TE Controller Operational Considerations . . . . . . . . 27 4.6. BFR Requirements for BIER-TE forwarding . . . . . . . . . 28
5.1. Bit position Assignments . . . . . . . . . . . . . . . . 27 5. BIER-TE Controller Operational Considerations . . . . . . . . 29
5.1.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . 27 5.1. Bit Position Assignments . . . . . . . . . . . . . . . . 29
5.1.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . 27 5.1.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . 29
5.1.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . 27 5.1.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . 28 5.1.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . 29
5.1.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . 29 5.1.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . 31
5.1.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . 29 5.1.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . 32
5.1.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . 30 5.1.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.8. Forward Routed adjacencies . . . . . . . . . . . . . 33 5.1.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . 33
5.1.8.1. Reducing bit positions . . . . . . . . . . . . . 33 5.1.8. Forward Routed adjacencies . . . . . . . . . . . . . 36
5.1.8.2. Supporting nodes without BIER-TE . . . . . . . . 34 5.1.8.1. Reducing bit positions . . . . . . . . . . . . . 36
5.1.9. Reuse of bit positions (without DNC) . . . . . . . . 34 5.1.8.2. Supporting nodes without BIER-TE . . . . . . . . 37
5.1.10. Summary of BP optimizations . . . . . . . . . . . . . 36 5.1.9. Reuse of bit positions (without DNC) . . . . . . . . 37
5.2. Avoiding duplicates and loops . . . . . . . . . . . . . . 37 5.1.10. Summary of BP optimizations . . . . . . . . . . . . . 38
5.2.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . 37 5.2. Avoiding duplicates and loops . . . . . . . . . . . . . . 39
5.2.2. Duplicates . . . . . . . . . . . . . . . . . . . . . 37 5.2.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3. Managing SI, sub-domains and BFR-ids . . . . . . . . . . 38 5.2.2. Duplicates . . . . . . . . . . . . . . . . . . . . . 40
5.3.1. Why SI and sub-domains . . . . . . . . . . . . . . . 38 5.3. Managing SI, sub-domains and BFR-ids . . . . . . . . . . 41
5.3.2. Assigning bits for the BIER-TE topology . . . . . . . 39 5.3.1. Why SI and sub-domains . . . . . . . . . . . . . . . 41
5.3.3. Assigning BFR-id with BIER-TE . . . . . . . . . . . . 40 5.3.2. Assigning bits for the BIER-TE topology . . . . . . . 42
5.3.4. Mapping from BFR to BitStrings with BIER-TE . . . . . 41 5.3.3. Assigning BFR-id with BIER-TE . . . . . . . . . . . . 43
5.3.5. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . 42 5.3.4. Mapping from BFR to BitStrings with BIER-TE . . . . . 44
5.3.6. Example bit allocations . . . . . . . . . . . . . . . 42 5.3.5. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . 45
5.3.6.1. With BIER . . . . . . . . . . . . . . . . . . . . 42 5.3.6. Example bit allocations . . . . . . . . . . . . . . . 45
5.3.6.2. With BIER-TE . . . . . . . . . . . . . . . . . . 43 5.3.6.1. With BIER . . . . . . . . . . . . . . . . . . . . 45
5.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 44 5.3.6.2. With BIER-TE . . . . . . . . . . . . . . . . . . 46
6. BIER-TE and Segment Routing . . . . . . . . . . . . . . . . . 45 5.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 47
7. Security Considerations . . . . . . . . . . . . . . . . . . . 46 6. Security Considerations . . . . . . . . . . . . . . . . . . . 48
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 47 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49
10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 47 9. Change log [RFC Editor: Please remove] . . . . . . . . . . . 50
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 57 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
11.1. Normative References . . . . . . . . . . . . . . . . . . 57 10.1. Normative References . . . . . . . . . . . . . . . . . . 62
11.2. Informative References . . . . . . . . . . . . . . . . . 57 10.2. Informative References . . . . . . . . . . . . . . . . . 63
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60 Appendix A. BIER-TE and Segment Routing . . . . . . . . . . . . 66
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 67
1. Overview 1. Overview
BIER-TE is based on architecture, terminology and packet formats with BIER-TE is based on the (non-TE) BIER architecture, terminology and
(non-TE) BIER as described in [RFC8279] and [RFC8296]. This document packet formats as described in [RFC8279] and [RFC8296]. This
describes BIER-TE in the expectation that the reader is familiar with document describes BIER-TE in the expectation that the reader is
these two documents. familiar with these two documents.
BIER-TE introduces a new semantic for bit positions (BP) that BIER-TE introduces a new semantic for "bit positions" (BP). They
indicate adjacencies, as opposed to BIER in which BPs indicate Bit- indicate adjacencies of the network topology, as opposed to (non-TE)
Forwarding Egress Routers (BFER). With BIER-TE, the BIFT of each BFR BIER in which BPs indicate "Bit-Forwarding Egress Routers" (BFER). A
is only populated with BP that are adjacent to the BFR in the BIER-TE BIER-TE packets BitString therefore indicates the edges of the (loop-
Topology. Other BPs are empty in the BIFT. The BFR replicate and free) tree that the packet is forwarded across by BIER-TE. With
forwards BIER packets to adjacent BPs that are set in the packet. BIER-TE, the "Bit Index Forwarding Table" (BIFT) of each "Bit
BPs are normally also cleared upon forwarding to avoid duplicates and Forwarding Router" (BFR) is only populated with BP that are adjacent
loops. This is detailed further below. to the BFR in the BIER-TE Topology. Other BPs are empty in the BIFT.
The BFR replicate and forwards BIER packets to adjacent BPs that are
set in the packet. BPs are normally also cleared upon forwarding to
avoid duplicates and loops.
BIER-TE can leverage BIER forwarding engines with little or no BIER-TE can leverage BIER forwarding engines with little or no
changes. It can also co-exist with BIER forwarding in the same changes. It can also co-exist with BIER forwarding in the same
domain, for example by using separate BIER sub-domains. Except for domain, for example by using separate BIER sub-domains. Except for
the optional routed adjacencies, BIER-TE does not require a BIER the optional routed adjacencies, BIER-TE does not require a BIER
routing underlay, and can therefore operate without depending on an routing underlay, and can therefore operate without depending on an
Interior Gateway Routing protocol (IGP). "Interior Gateway Routing protocol" (IGP).
As it operates on the same per-packet stateless forwarding As it operates on the same per-packet stateless forwarding
principles, BIER-TE can also be a good fit to support multicast path principles, BIER-TE can also be a good fit to support multicast path
steering in Segment Routing (SR) networks. steering in "Segment Routing" (SR) networks ([RFC8402]).
This document is structured as follows: This document is structured as follows:
* Section 2 introduces BIER-TE with two reference forwarding * Section 2 introduces BIER-TE with two forwarding examples,
examples, followed by an introduction of the new concepts of the followed by an introduction of the new concepts of the BIER-TE
BIER-TE (overlay) topology and finally a summary of the (overlay) topology and finally a summary of the relationship
relationship between BIER and BIER-TE and a discussion of between BIER and BIER-TE and a discussion of accelerated hardware
accelerated hardware forwarding. forwarding.
* Section 3 describes the components of the BIER-TE architecture, * Section 3 describes the components of the BIER-TE architecture,
Flow overlay, BIER-TE layer with the BIER-TE control plane Flow overlay, BIER-TE layer with the BIER-TE control plane
(including the BIER-TE controller) and BIER-TE forwarding plane, (including the BIER-TE controller) and BIER-TE forwarding plane,
and the routing underlay. and the routing underlay.
* Section 4 specifies the behavior of the BIER-TE forwarding plane * Section 4 specifies the behavior of the BIER-TE forwarding plane
with the different type of adjacencies and possible variations of with the different type of adjacencies and possible variations of
BIER-TE forwarding pseudocode, and finally the mandatory and BIER-TE forwarding pseudocode, and finally the mandatory and
optional requirements. optional requirements.
* Section 5 describes operational considerations for the BIER-TE * Section 5 describes operational considerations for the BIER-TE
controller, foremost how the BIER-TE controller can optimize the controller, foremost how the BIER-TE controller can optimize the
use of BP by using specific type of BIER-TE adjacencies for use of BP by using specific type of BIER-TE adjacencies for
different type of topological situations, but also how to assign different type of topological situations, but also how to assign
bits to avoid loops and duplicates (which in BIER-TE does not come bits to avoid loops and duplicates (which in BIER-TE does not come
for free), and finally how SI, sub-domains and BFR-ids can be for free), and finally how "Set Identifier" (SI), "sub-domain"
managed by a BIER-TE controller, examples and summary. (SD) and BFR-ids can be managed by a BIER-TE controller, examples
and summary.
* Section 6 concludes the technology specific sections of document * Appendix A concludes the technology specific sections of the
by further relating BIER-TE to Segment Routing (SR). document by further relating BIER-TE to SR.
Note that related work, [I-D.ietf-roll-ccast] uses Bloom filters Note that related work, [I-D.ietf-roll-ccast] uses Bloom filters
[Bloom70] to represent leaves or edges of the intended delivery tree. [Bloom70] to represent leaves or edges of the intended delivery tree.
Bloom filters in general can support larger trees/topologies with Bloom filters in general can support larger trees/topologies with
fewer addressing bits than explicit BitStrings, but they introduce fewer addressing bits than explicit BitStrings, but they introduce
the heuristic risk of false positives and cannot clear bits in the the heuristic risk of false positives and cannot clear bits in the
BitString during forwarding to avoid loops. For these reasons, BIER- BitString during forwarding to avoid loops. For these reasons, BIER-
TE uses explicit BitStrings like BIER. The explicit BitStrings of TE uses explicit BitStrings like BIER. The explicit BitStrings of
BIER-TE can also be seen as a special type of Bloom filter, and this BIER-TE can also be seen as a special type of Bloom filter, and this
is how related work [ICC] describes it. is how related work [ICC] describes it.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119], [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Introduction 2. Introduction
2.1. Basic Examples 2.1. Basic Examples
BIER-TE forwarding is best introduced with simple examples. BIER-TE forwarding is best introduced with simple examples. These
examples use formal terms defined later in the document (Figure 4),
including forward_connected(), forward_routed() and local_decap().
BIER-TE Topology: BIER-TE Topology:
Diagram: Diagram:
p5 p6 p5 p6
--- BFR3 --- --- BFR3 ---
p3/ p13 \p7 p15 p3/ p13 \p7 p15
BFR1 ---- BFR2 BFR5 ----- BFR6 BFR1 ---- BFR2 BFR5 ----- BFR6
p1 p2 p4\ p14 /p10 p11 p12 p1 p2 p4\ p14 /p10 p11 p12
--- BFR4 --- --- BFR4 ---
p8 p9 p8 p9
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT): (simplified) BIER-TE Bit Index Forwarding Tables (BIFT):
BFR1: p1 -> local_decap BFR1: p1 -> local_decap()
p2 -> forward_connected() to BFR2 p2 -> forward_connected() to BFR2
BFR2: p1 -> forward_connected() to BFR1 BFR2: p1 -> forward_connected() to BFR1
p5 -> forward_connected() to BFR3 p5 -> forward_connected() to BFR3
p8 -> forward_connected() to BFR4 p8 -> forward_connected() to BFR4
BFR3: p3 -> forward_connected() to BFR2 BFR3: p3 -> forward_connected() to BFR2
p7 -> forward_connected() to BFR5 p7 -> forward_connected() to BFR5
p13 -> local_decap p13 -> local_decap()
BFR4: p4 -> forward_connected() to BFR2 BFR4: p4 -> forward_connected() to BFR2
p10 -> forward_connected() to BFR5 p10 -> forward_connected() to BFR5
p14 -> local_decap p14 -> local_decap()
BFR5: p6 -> forward_connected() to BFR3 BFR5: p6 -> forward_connected() to BFR3
p9 -> forward_connected() to BFR4 p9 -> forward_connected() to BFR4
p12 -> forward_connected() to BFR6 p12 -> forward_connected() to BFR6
BFR6: p11 -> forward_connected() to BFR5 BFR6: p11 -> forward_connected() to BFR5
p15 -> local_decap p15 -> local_decap()
Figure 1: BIER-TE basic example Figure 1: BIER-TE basic example
Consider the simple network in the above BIER-TE overview example Consider the simple network in the above BIER-TE overview example
picture with 6 BFRs. p1...p14 are the bit positions (BP) used. All picture with 6 BFRs. p1...p15 are the bit positions used. All BFRs
BFRs can act as an ingress BFR (BFIR), BFR1, BFR3, BFR4 and BFR6 can can act as an ingress BFR (BFIR), BFR1, BFR3, BFR4 and BFR6 can also
also be egress BFRs (BFERs). Forward_connected() is the name for be BFERs. Forward_connected() is the name for adjacencies that are
adjacencies that are representing subnet adjacencies of the network. representing subnet adjacencies of the network. Local_decap() is the
Local_decap() is the name of the adjacency to decapsulate BIER-TE name of the adjacency to decapsulate BIER-TE packets and pass their
packets and pass their payload to higher layer processing. payload to higher layer processing.
Assume a packet from BFR1 should be sent via BFR4 to BFR6. This Assume a packet from BFR1 should be sent via BFR4 to BFR6. This
requires a BitString (p2,p8,p10,p12,p15). When this packet is requires a BitString (p2,p8,p10,p12,p15). When this packet is
examined by BIER-TE on BFR1, the only bit position from the BitString examined by BIER-TE on BFR1, the only bit position from the BitString
that is also set in the BIFT is p2. This will cause BFR1 to send the that is also set in the BIFT is p2. This will cause BFR1 to send the
only copy of the packet to BFR2. Similarly, BFR2 will forward to only copy of the packet to BFR2. Similarly, BFR2 will forward to
BFR4 because of p8, BFR4 to BFR5 because of p10 and BFR5 to BFR6 BFR4 because of p8, BFR4 to BFR5 because of p10 and BFR5 to BFR6
because of p12. p15 finally makes BFR6 receive and decapsulate the because of p12. p15 finally makes BFR6 receive and decapsulate the
packet. packet.
To send in addition to BFR6 via BFR4 also a copy to BFR3, the To send a copy to BFR6 via BFR4 and also a copy to BFR3, the
BitString needs to be (p2,p5,p8,p10,p12,p13). When this packet is BitString needs to be (p2,p5,p8,p10,p12,p13,p15). When this packet
examined by BFR2, p5 causes one copy to be sent to BFR3 and p8 one is examined by BFR2, p5 causes one copy to be sent to BFR3 and p8 one
copy to BFR4. When BFR3 receives the packet, p13 will cause it to copy to BFR4. When BFR3 receives the packet, p13 will cause it to
receive and decapsulate the packet. receive and decapsulate the packet.
If instead the BitString was (p2,p6,p8,p10,p12,p13,p15), the packet If instead the BitString was (p2,p6,p8,p10,p12,p13,p15), the packet
would be copied by BFR5 towards BFR3 because of p6 instead of being would be copied by BFR5 towards BFR3 because of p6 instead of being
copied by BFR2 to BFR3 because of p5 in the prior case. This is copied by BFR2 to BFR3 because of p5 in the prior case. This is
showing the ability of the shown BIER-TE Topology to make the traffic showing the ability of the shown BIER-TE Topology to make the traffic
pass across any possible path and be replicated where desired. pass across any possible path and be replicated where desired.
BIER-TE has various options to minimize BP assignments, many of which BIER-TE has various options to minimize BP assignments, many of which
are based on assumptions about the required multicast traffic paths are based on out-of-band knowledge about the required multicast
and bandwidth consumption in the network. traffic paths and bandwidth consumption in the network, such as from
pre-deployment planning.
The following picture shows a modified example, in which Rtr2 and Figure 2 shows a modified example, in which Rtr2 and Rtr5 are assumed
Rtr5 are assumed not to support BIER-TE, so traffic has to be unicast not to support BIER-TE, so traffic has to be unicast encapsulated
encapsulated across them. To emphasize non-L2, but routed/tunneled across them. To emphasize non-L2, but routed/tunneled forwarding of
forwarding of BIER-TE packets, these adjacencies are called BIER-TE packets, these adjacencies are called "forward_routed".
"forward_routed". Otherwise there is no difference in their Otherwise, there is no difference in their processing over the
processing over the aforementioned "forward_connected" adjacencies. aforementioned forward_connected() adjacencies.
In addition, bits are saved in the following example by assuming that In addition, bits are saved in the following example by assuming that
BFR1 only needs to be BFIR but not BFER or transit BFR. BFR1 only needs to be BFIR but not BFER or transit BFR.
BIER-TE Topology: BIER-TE Topology:
Diagram: Diagram:
p1 p3 p7 p1 p3 p7
....> BFR3 <.... p5 ....> BFR3 <.... p5
........ ........> ........ ........>
BFR1 (Rtr2) (Rtr5) BFR6 BFR1 (Rtr2) (Rtr5) BFR6
........ ........> ........ ........> p9
....> BFR4 <.... p6 ....> BFR4 <.... p6
p2 p4 p8 p2 p4 p8
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT): (simplified) BIER-TE Bit Index Forwarding Tables (BIFT):
BFR1: p1 -> forward_routed() to BFR3 BFR1: p1 -> forward_routed() to BFR3
p2 -> forward_routed() to BFR4 p2 -> forward_routed() to BFR4
BFR3: p3 -> local_decap BFR3: p3 -> local_decap()
p5 -> forward_routed() to BFR6 p5 -> forward_routed() to BFR6
BFR4: p4 -> local_decap BFR4: p4 -> local_decap()
p6 -> forward_routed() to BFR6 p6 -> forward_routed() to BFR6
BFR6: p5 -> local_decap BFR6: p7 -> forward_routed() to BFR3
p6 -> local_decap
p7 -> forward_routed() to BFR3
p8 -> forward_routed() to BFR4 p8 -> forward_routed() to BFR4
p9 -> local_decap()
Figure 2: BIER-TE basic overlay example Figure 2: BIER-TE basic overlay example
To send a BIER-TE packet from BFR1 via BFR3 to BFR6, the BitString is To send a BIER-TE packet from BFR1 via BFR3 to be received by BFR6,
(p1,p5). From BFR1 via BFR4 to BFR6 it is (p2,p6). A packet from the BitString is (p1,p5,p9). From BFR1 via BFR4 to be received by
BFR1 to BFR3,BFR4 and from BFR3 to BFR6 uses (p1,p2,p3,p4,p5). A BFR6, the BitString is (p2,p6,p9). A packet from BFR1 to be received
packet from BFR1 to BFR3,BFR4 and from BFR4 to BFR uses by BFR3,BFR4 and from BFR3 to be received by BFR6 uses
(p1,p2,p3,p4,p6). A packet from BFR1 to BFR4, and from BFR4 to BFR6 (p1,p2,p3,p4,p5,p9). A packet from BFR1 to be received by BFR3,BFR4
and from BFR6 to BFR3 uses (p2,p3,p4,p6,p7). A packet from BFR1 to and from BFR4 to be received by BFR6 uses (p1,p2,p3,p4,p6,p9). A
BFR3, and from BFR3 to BFR6 and from BFR6 to BFR4 uses packet from BFR1 to be received by BFR4, and from BFR4 to be received
(p1,p3,p4,p5,p8). by BFR6 and from there to be received by BFR3 uses
(p2,p3,p4,p6,p7,p9). A packet from BFR1 to be received by BFR3, and
from BFR3 to be received by BFR6 there to be received by BFR4 uses
(p1,p3,p4,p5,p8,p9).
2.2. BIER-TE Topology and adjacencies 2.2. BIER-TE Topology and adjacencies
The key new component in BIER-TE compared to (non-TE) BIER is the The key new component in BIER-TE compared to (non-TE) BIER is the
BIER-TE topology as introduced through the two examples in BIER-TE topology as introduced through the two examples in
Section 2.1. It is used to control where replication can or should Section 2.1. It is used to control where replication can or should
happen and how to minimize the required number of BP for adjacencies. happen and how to minimize the required number of BP for adjacencies.
The BIER-TE Topology consists of the BIFTs of all the BFR and can The BIER-TE Topology consists of the BIFTs of all the BFR and can
also be expressed as a directed graph where the edges are the also be expressed as a directed graph where the edges are the
adjacencies between the BFR labelled with the BP used for the adjacencies between the BFRs labelled with the BP used for the
adjacency. Adjacencies are naturally unidirectional. BP can be adjacency. Adjacencies are naturally unidirectional. BP can be
reused across multiple adjacencies as long as this does not lead to reused across multiple adjacencies as long as this does not lead to
undesired duplicates or loops as explained further down in the text. undesired duplicates or loops as explained in Section 5.2.
If the BIER-TE topology represents (a subset of) the underlying If the BIER-TE topology represents (a subset of) the underlying
(layer 2) topology of the network as shown in the first example, this (layer 2) topology of the network as shown in the first example, this
may be called a "native" BIER-TE topology. A topology consisting may be called a "native" BIER-TE topology. A topology consisting
only of "forward_routed" adjacencies as shown in the second example only of "forward_routed" adjacencies as shown in the second example
may be called an "overlay" BIER-TE topology. A BIER-TE topology with may be called an "overlay" BIER-TE topology. A BIER-TE topology with
both "forward_connected" and "forward_routed" adjacencies may be both forward_connected() and forward_routed() adjacencies may be
called a "hybrid" BIER-TE topology. called a "hybrid" BIER-TE topology.
2.3. Relationship to BIER 2.3. Relationship to BIER
BIER-TE is designed so that is forwarding plane is a simple extension BIER-TE is designed so that its forwarding plane is a simple
to the (non-TE) BIER forwarding plane, hence allowing for it to be extension to the (non-TE) BIER forwarding plane, hence allowing for
added to BIER deployments where it can be beneficial. it to be added to BIER deployments where it can be beneficial.
BIER-TE is also intended as an option to expand the BIER architecture BIER-TE is also intended as an option to expand the BIER architecture
into deployments where (non-TE) BIER may not be the best fit, such as into deployments where (non-TE) BIER may not be the best fit, such as
statically provisioned networks with needs for path steering but statically provisioned networks with needs for path steering but
without desire for distributed routing protocols. without desire for distributed routing protocols.
1. BIER-TE inherits the following aspects from BIER unchanged: 1. BIER-TE inherits the following aspects from BIER unchanged:
1. The fundamental purpose of per-packet signaled packet 1. The fundamental purpose of per-packet signaled replication
replication and delivery via a BitString. and delivery via a BitString.
2. The overall architecture consisting of three layers, flow 2. The overall architecture consisting of three layers, flow
overlay, BIER(-TE) layer and routing underlay. overlay, BIER(-TE) layer and routing underlay.
3. The supportable encapsulations, [RFC8296] or other (future) 3. The supported encapsulations [RFC8296].
encapsulations.
4. The semantic of all [RFC8296] header elements used by the 4. The semantic of all [RFC8296] header elements used by the
BIER-TE forwarding plane other than the semantic of the BP in BIER-TE forwarding plane other than the semantic of the BP in
the BitString. the BitString.
5. The BIER forwarding plane, with the exception of how bits 5. The BIER forwarding plane, except for how bits have to be
have to be cleared during replication. cleared during replication.
2. BIER-TE has the following key changes with respect to BIER: 2. BIER-TE has the following key changes with respect to BIER:
1. In BIER, bits in the BitString of a BIER packet header 1. In BIER, bits in the BitString of a BIER packet header
indicate a BFER and bits in the BIFT indicate the BIER indicate a BFER and bits in the BIFT indicate the BIER
control plane calculated next-hop toward that BFER. In BIER- control plane calculated next-hop toward that BFER. In BIER-
TE, bits in the BitString of a BIER packet header indicate an TE, a bit in the BitString of a BIER packet header indicates
adjacency in the BIER-TE topology, and only the BFRs that are an adjacency in the BIER-TE topology, and only the BFR that
the upstream of this adjacency have this bit populated with is the upstream of that adjacency has its BP populated with
the adjacency in their BIFT. the adjacency in its BIFT.
2. In BIER, the implied reference option for the core part of 2. In BIER, the implied reference option for the core part of
the BIER layer control plane are the BIER extensions for the BIER layer control plane are the BIER extensions for
distributed routing protocols, such as those standardized in distributed routing protocols. This includes ISIS/OSPF
ISIS/OSPF extensions for BIER, [RFC8401] and [RFC8444]. The extensions for BIER, [RFC8401] and [RFC8444].
reference option for the core part of the BIER-TE control
plane is the BIER-TE controller. Nevertheless, both BIER and 3. The reference option for the core part of the BIER-TE control
BIER-TE BIFT forwarding plane state could equally be plane is the BIER-TE controller. Nevertheless, both the BIER
and BIER-TE BIFTs forwarding plane state could equally be
populated by any mechanism. populated by any mechanism.
3. Assuming the reference options for the control plane, BIER-TE 4. Assuming the reference options for the control plane, BIER-TE
replaces in-network autonomous path calculation by explicit replaces in-network autonomous path calculation by explicit
paths calculated by the BIER-TE controller. paths calculated by the BIER-TE controller.
3. The following elements/functions described in the BIER 3. The following elements/functions described in the BIER
architecture are not required by the BIER-TE architecture: architecture are not required by the BIER-TE architecture:
1. BIRTs are not required on BFRs for BIER-TE when using a BIER- 1. "Bit Index Routing Tables" (BIRTs) are not required on BFRs
TE controller because the controller can directly populate for BIER-TE when using a BIER-TE controller because the
the BIFTs. In BIER, BIRTs are populated by the distributed controller can directly populate the BIFTs. In BIER, BIRTs
routing protocol support for BIER, allowing BFRs to populate are populated by the distributed routing protocol support for
their BIFTs locally from their BIRTs. Other BIER-TE control BIER, allowing BFRs to populate their BIFTs locally from
plane or management plane options may introduce requirements their BIRTs. Other BIER-TE control plane or management plane
for BIRTs for BIER-TE BFRs. options may introduce requirements for BIRTs for BIER-TE
BFRs.
2. The BIER-TE layer forwarding plane does not require BFRs to 2. The BIER-TE layer forwarding plane does not require BFRs to
have a unique BP and therefore also no unique BFR-id. See have a unique BP and therefore also no unique BFR-id. See
for example See Section 5.1.3. Section 5.1.3.
3. Identification of BFRs by the BIER-TE control plane is 3. Identification of BFRs by the BIER-TE control plane is
outside the scope of this specification. Whereas the BIER outside the scope of this specification. Whereas the BIER
control plane uses BFR-ids in its BFR to BFR signaling, a control plane uses BFR-ids in its BFR to BFR signaling, a
BIER-TE controller may choose any form of identification BIER-TE controller may choose any form of identification
deemed appropriate. deemed appropriate.
4. BIER-TE forwarding does not use the BFR-id field of the BIER 4. BIER-TE forwarding does not require the BFIR-id field of the
packet header. BIER packet header.
4. Co-existence of BIER and BIER-TE in the same network requires the 4. Co-existence of BIER and BIER-TE in the same network requires the
following: following:
1. The BIER/BIER-TE packet header needs to allow addressing both 1. The BIER/BIER-TE packet header needs to allow addressing both
BIER and BIER-TE BIFT. Depending on the encapsulation BIER and BIER-TE BIFTs. Depending on the encapsulation
option, the same SD may or may not be reusable across BIER option, the same SD may or may not be reusable across BIER
and BIER-TE. See Section 4.3. In either case, a packet is and BIER-TE. See Section 4.3. In either case, a packet is
always only forwarded end-to-end via BIER or via BIER-TE always only forwarded end-to-end via BIER or via BIER-TE
(ships in the nights forwarding). (ships in the nights forwarding).
2. BIER-TE deployments will have to assign BFR-ids to BFRs and 2. BIER-TE deployments will have to assign BFR-ids to BFRs and
insert them into the BFR-id field of BIER packet headers as insert them into the BFIR-id field of BIER packet headers as
BIER does, whenever the deployment uses (unchanged) BIER does, whenever the deployment uses (unchanged)
components developed for BIER that use BFR-id, such as components developed for BIER that use BFR-id, such as
multicast flow overlays or BIER layer control plane elements. multicast flow overlays or BIER layer control plane elements.
See also Section 5.3.3. See also Section 5.3.3.
2.4. Accelerated/Hardware forwarding comparison 2.4. Accelerated/Hardware forwarding comparison
Forwarding of BIER-TE is designed to easily build/program common BIER-TE forwarding rules, especially the BitString parsing are
forwarding hardware with BIER. The pseudocode in Section 4.4 shows designed to be as close as possible to those of BIER in the
how existing (non-TE) BIER/BIFT forwarding can be modified to support expectation that this eases the programming of BIER-TE forwarding
the REQUIRED BIER-TE forwarding functionality, by using BIER BIFT's code and/or BIER-TE forwarding hardware on platforms supporting BIER.
"Forwarding Bit Mask" (F-BM): Only the clearing of bits to avoid The pseudocode in Section 4.4 shows how existing (non-TE) BIER/BIFT
duplicate packets to a BFR's neighbor is skipped in BIER-TE forwarding can be modified to support the required BIER-TE forwarding
forwarding because it is not necessary and could not be done when functionality (Section 4.6), by using BIER BIFT's "Forwarding Bit
using BIER F-BM. Mask" (F-BM): Only the clearing of bits to avoid duplicate packets to
a BFR's neighbor is skipped in BIER-TE forwarding because it is not
necessary and could not be done when using BIER F-BM.
Whether to use BIER or BIER-TE forwarding is simply a choice of the Whether to use BIER or BIER-TE forwarding is simply a choice of the
mode of the BIFT indicated by the packet (BIER or BIER-TE BIFT). mode of the BIFT indicated by the packet (BIER or BIER-TE BIFT).
This is determined by the BFR configuration for the encapsulation, This is determined by the BFR configuration for the encapsulation,
see Section 4.3. see Section 4.3.
3. Components 3. Components
BIER-TE can be thought of being constituted from the same three BIER-TE can be thought of being constituted from the same three
layers as BIER: The "multicast flow overlay", the "BIER layer" and layers as BIER: The "multicast flow overlay", the "BIER layer" and
skipping to change at page 12, line 12 skipping to change at page 12, line 12
"BIER layer" is constituted from the "BIER-TE forwarding plane" and "BIER layer" is constituted from the "BIER-TE forwarding plane" and
the "BIER-TE control plane" represent by the "BIER-TE Controller". the "BIER-TE control plane" represent by the "BIER-TE Controller".
<------BGP/PIM-----> <------BGP/PIM----->
|<-IGMP/PIM-> multicast flow <-PIM/IGMP->| |<-IGMP/PIM-> multicast flow <-PIM/IGMP->|
overlay overlay
BIER-TE [BIER-TE Controller] <=> [BIER-TE Topology] BIER-TE [BIER-TE Controller] <=> [BIER-TE Topology]
control ^ ^ ^ control ^ ^ ^
plane / | \ BIER-TE control protocol plane / | \ BIER-TE control protocol
| | | e.g. YANG/Netconf/RestConf | | | e.g. YANG/NETCONF/RESTCONF
| | | PCEP/... | | | PCEP/...
v v v v v v
Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr
|<----------------->| |<----------------->|
BIER-TE forwarding plane BIER-TE forwarding plane
|<- BIER-TE domain->| |<- BIER-TE domain->|
|<--------------------->| |<--------------------->|
Routing underlay Routing underlay
Figure 3: BIER-TE architecture Figure 3: BIER-TE architecture
3.1. The Multicast Flow Overlay 3.1. The Multicast Flow Overlay
The Multicast Flow Overlay has the same role as described for BIER in The Multicast Flow Overlay has the same role as described for BIER in
[RFC8279], Section 4.3. See also Section 3.2.1.2. [RFC8279], Section 4.3. See also Section 3.2.1.2.
When a BIER-TE controller is used, then the signaling for the
Multicast Flow Overlay may also be preferred to operate through a
central point of control. For BGP based overlay flow services such
as "Multicast VPN Using BIER" ([RFC8556]) this can be achieved by
making the BIER-TE controller operate as a BGP Route Reflector
([RFC4456]) and combining it with signaling through BGP or a
different protocol for the BIER-TE controller calculated BitStrings.
See Section 3.2.1.2 and Section 5.3.4.
3.2. The BIER-TE Control Plane 3.2. The BIER-TE Control Plane
In the (non-TE) BIER architecture [RFC8279], the BIER control plane In the (non-TE) BIER architecture [RFC8279], the BIER control plane
is not explicitly separated from the BIER forwarding plane, but is not explicitly separated from the BIER forwarding plane, but
instead their functions are summarized together in Section 4.2. instead their functions are summarized together in Section 4.2.
Example standardized options for the BIER control plane include ISIS/ Example standardized options for the BIER control plane include ISIS/
OSPF extensions for BIER, [RFC8401] and [RFC8444]. OSPF extensions for BIER, [RFC8401] and [RFC8444].
For BIER-TE, the control plane includes at minimum the following For BIER-TE, the control plane includes at minimum the following
functionality. functionality.
1. During initial provisioning of the network and/or during 1. BIER-TE topology control: During initial provisioning of the
modifications of its topology and/or services: protocols and/or network and/or during modifications of its topology and/or
procedures to establish BIER-TE BIFTs: services, the protocols and/or procedures to establish BIER-TE
BIFTs:
1. Determine the desired BIER-TE topology for a BIER-TE sub- 1. Determine the desired BIER-TE topology for a BIER-TE sub-
domains: the native and/or overlay adjacencies that are domains: the native and/or overlay adjacencies that are
assigned to BPs. assigned to BPs. Topology discovery is discussed in
Section 3.2.1.1 and the various aspects of the BIER-TE
controllers determinations about the topology are discussed
throughout Section 5
2. Determine the per-BFR BIFT from the BIER-TE topology. 2. Determine the per-BFR BIFT from the BIER-TE topology. This is
achieved by simply extracting the adjacencies of the BFR from
the BIER-TE topology and populating the BFRs BIFT with them.
3. Optionally assign BFR-ids to BFIRs for later insertion into 3. Optionally assign BFR-ids to BFIRs for later insertion into
BIER-TE headers on BFIRs. Alternatively, bfir-id in BIER BIER headers on BFIRs as BFIR-id. Alternatively, BFIR-id in
packet headers may be managed solely by the flow overlay BIER packet headers may be managed solely by the flow overlay
layer and/or be unused. layer and/or be unused. This is discussed in Section 5.3.3.
4. Install/update the BIFTs into the BFRs and optionally BFR-ids 4. Install/update the BIFTs into the BFRs and optionally BFR-ids
into BFIRs. into BFIRs. This is discussed in Section 3.2.1.1.
2. During operations of the network: Protocols and/or procedures to 2. BIER-TE tree control: During operations of the network,
support creation/change/removal of overlay flows on BFIRs: protocols and/or procedures to support creation/change/removal of
overlay flows on BFIRs:
1. Process the BIER-TE requirements for the multicast overlay 1. Process the BIER-TE requirements for the multicast overlay
flow: BFIR and BFERs of the flow as well as policies for the flow: BFIR and BFERs of the flow as well as policies for the
path selection of the flow. path selection of the flow. This is discussed in Section 3.5.
2. Determine the BitStrings and optionally Entropy. 2. Determine the BitStrings and optionally Entropy. This is
discussed in Section 3.2.1.2, Section 3.5 and Section 5.3.4.
3. Install state on the BFIR to impose the desired BIER packet 3. Install state on the BFIR to impose the desired BIER packet
header(s) for packets of the overlay flow. header(s) for packets of the overlay flow. Different aspects
of this and the next point are discussed throughout
Section 3.2.1 and in Section 4.3, but the main responsibility
of these two points is with the Multicast Flow Overlay
(Section 3.1), which is architecturally inherited from BIER.
4. Install the necessary state on the BFERs to decapsulate the 4. Install the necessary state on the BFERs to decapsulate the
BIER packet header and properly dispatch its payload. BIER packet header and properly dispatch its payload.
3.2.1. The BIER-TE Controller 3.2.1. The BIER-TE Controller
Notwithstanding other options, this architecture describes the BIER [RFC-Editor: the following text has three references to anchors
control plane as shown in Figure 3 to consists of: topology-control, topology-control-1 and tree-control.
Unfortunately, XMLv2 does not offer any tagging that reasonable
references are generated (i had this problem already in RFCs last
year. Please make sure there are useful-to-read cross-references in
the RFC in these three places after you convert to XMLv3.]
* A single centralized BIER-TE controller. This architecture describes the BIER-TE control plane as shown in
Figure 3 to consist of:
* Data-models and protocols to communicate between controller and * A BIER-TE controller.
BFRs in step 1, such as YANG/Netconf/RestConf.
* Protocols to communicate between controller and BFIR in step 2, * BFR data-models and protocols to communicate between controller
such as BIER-TE extensions for [RFC5440]. and BFRs in support of BIER-TE topology control (Section 3.2),
such as YANG/NETCONF/RESTCONF ([RFC7950]/[RFC6241]/[RFC8040]).
The (non-TE) BIER control plane could equally be implemented without * BFR data-models and protocols to communicate between controller
any active dynamic components by an operator via CLI on the BFRs. In and BFIR in support of BIER-TE tree control (Section 3.2), such as
that case, operator configured local policy on the BFIR would have to BIER-TE extensions for [RFC5440].
determine how to set the appropriate BIER header fields. The BIER-TE
control plane could also be decentralized and/or distributed, but The single, centralized BIER-TE controller is used in this document
this document does not consider any additional protocols and/or as reference option for the BIER-TE control plane but other options
procedures which would then be necessary to coordinate its entities are equally feasible. The BIER-TE control plane could equally be
to achieve the above described functionality. implemented without automated configuration/protocols, by an operator
via CLI on the BFRs. In that case, operator configured local policy
on the BFIR would have to determine how to set the appropriate BIER
header fields. The BIER-TE control plane could also be decentralized
and/or distributed, but this document does not consider any
additional protocols and/or procedures which would then be necessary
to coordinate its (distributed/decentralized) entities to achieve the
above described functionality.
3.2.1.1. BIER-TE Topology discovery and creation 3.2.1.1. BIER-TE Topology discovery and creation
Step 1.1 includes network topology discovery and BIER-TE topology The first item of BIER-TE topology control (Section 3.2, Paragraph 3,
Item 2.2.1) includes network topology discovery and BIER-TE topology
creation. The latter describes the process by which a Controller creation. The latter describes the process by which a Controller
determines which routers are to be configured as BFR and the determines which routers are to be configured as BFRs and the
adjacencies between them. adjacencies between them.
In statically managed networks, such as in industrial environments, In statically managed networks, such as in industrial environments,
both discovery and creation can be a manual/offline process. both discovery and creation can be a manual/offline process.
In other networks, topology discovery may rely on protocols including In other networks, topology discovery may rely on protocols including
extending a Link-State-Protocol (LSP) based IGP into the BIER-TE extending a "Link-State-Protocol" based IGP into the BIER-TE
controller itself, [RFC7752] (BGP-LS) or [RFC8345] (Yang topology) as controller itself, [RFC7752] (BGP-LS) or [RFC8345] (YANG topology) as
well as BIER-TE specific methods, for example via well as BIER-TE specific methods, for example via
[I-D.ietf-bier-te-yang]. These options are non-exhaustive. [I-D.ietf-bier-te-yang]. These options are non-exhaustive.
Dynamic creation of the BIER-TE topology can be as easy as mapping Dynamic creation of the BIER-TE topology can be as easy as mapping
the network topology 1:1 to the BIER-TE topology by assigning a BP the network topology 1:1 to the BIER-TE topology by assigning a BP
for every network subnet adjacency. In larger networks, it likely for every network subnet adjacency. In larger networks, it likely
involves more complex policy and optimization decisions including how involves more complex policy and optimization decisions including how
to minimize the number of BP required and how to assign BP across to minimize the number of BPs required and how to assign BPs across
different BitStrings to minimize the number of duplicate packets different BitStrings to minimize the number of duplicate packets
across links when delivering an overlay flow to BFER using different across links when delivering an overlay flow to BFER using different
SIs/BitStrings. These topics are discussed in Section 5. SIs/BitStrings. These topics are discussed in Section 5.
When the BIER-TE topology is determined, the BIER-TE Controller then When the BIER-TE topology is determined, the BIER-TE Controller then
pushes the BitPositions/adjacencies to the BIFT of the BFRs. On each pushes the BitPositions/adjacencies to the BIFT of the BFRs. On each
BFR only those SI:BitPositions are populated that are adjacencies to BFR only those SI:BitPositions are populated that are adjacencies to
other BFRs in the BIER-TE topology. other BFRs in the BIER-TE topology.
Communications between the BIER-TE Controller and BFRs (beside Communications between the BIER-TE Controller and BFRs for both BIER-
topology discovery) is ideally via standardized protocols and data- TE topology control and BIER-TE tree control is ideally via
models such as Netconf/RestConf/Yang/PCEP. Vendor-specific CLI on standardized protocols and data-models such as NETCONF/RESTCONF/YANG/
the BFRs is also an option (as in many other SDN solutions lacking PCEP. Vendor-specific CLI on the BFRs is also an option (as in many
definition of standardized data model). other SDN solutions lacking definition of standardized data models).
3.2.1.2. Engineered Trees via BitStrings 3.2.1.2. Engineered Trees via BitStrings
In BIER, the same set of BFER in a single sub-domain is always In BIER, the same set of BFER in a single sub-domain is always
encoded as the same BitString. In BIER-TE, the BitString used to encoded as the same BitString. In BIER-TE, the BitString used to
reach the same set of BFER in the same sub-domain can be different reach the same set of BFER in the same sub-domain can be different
for different overlay flows because the BitString encodes the paths for different overlay flows because the BitString encodes the paths
towards the BFER, so the BitStrings from different BFIR to the same towards the BFER, so the BitStrings from different BFIR to the same
set of BFER will often be different. Likewise, the BitString from set of BFER will often be different. Likewise, the BitString from
the same BFIR to the same set of BFER can be different for different the same BFIR to the same set of BFER can be different for different
skipping to change at page 15, line 31 skipping to change at page 16, line 28
the details of which are out of scope for this document. It can also the details of which are out of scope for this document. It can also
more slowly react by recalculating the BitStrings of affected more slowly react by recalculating the BitStrings of affected
multicast flows. This reaction is slower than the FRR procedure multicast flows. This reaction is slower than the FRR procedure
because the BIER-TE Controller needs to receive link/node up/down because the BIER-TE Controller needs to receive link/node up/down
indications, recalculate the desired BitStrings and push them down indications, recalculate the desired BitStrings and push them down
into the BFIRs. With FRR, this is all performed locally on a BFR into the BFIRs. With FRR, this is all performed locally on a BFR
receiving the adjacency up/down notification. receiving the adjacency up/down notification.
3.3. The BIER-TE Forwarding Plane 3.3. The BIER-TE Forwarding Plane
The BIER-TE Forwarding Plane constitutes of the following components: [RFC-editor Q: "is constituted from" / "consists of" / "composed
from..." ???]
1. On BFIR, imposition of BIER header for packets from overlay The BIER-TE Forwarding Plane is constituted from the following
components:
1. On a BFIR, imposition of the BIER header for packets from overlay
flows. This is driven by a combination of state established by flows. This is driven by a combination of state established by
the BIER-TE control plane and/or the multicast flow overlay as the BIER-TE control plane and/or the multicast flow overlay as
explained in Section 3.1. explained in Section 3.1.
2. On BFR (including BFIR and BFER), forwarding/replication of BIER 2. On BFRs (including BFIR and BFER), forwarding/replication of BIER
packets according to their BitString as explained below and packets according to their SD, SI, "BitStringLength" (BSL),
optionally Entropy. Processing of other BIER header fields such BitString and optionally Entropy fields as explained in
as DSCP is outside the scope of this document. Section 4. Processing of other BIER header fields such as DSCP
is outside the scope of this document.
3. On BFER, removal of BIER header and dispatching of the payload 3. On BFERs, removal of the BIER header and dispatching of the
according to state created by the BIER-TE control plane and/or payload according to state created by the BIER-TE control plane
overlay layer. and/or overlay layer.
When the BIER-TE Forwarding Plane receives a packet, it simply looks When the BIER-TE Forwarding Plane receives a packet, it simply looks
up the bit positions that are set in the BitString of the packet in up the bit positions that are set in the BitString of the packet in
the Bit Index Forwarding Table (BIFT) that was populated by the BIER- the BIFT that was populated by the BIER-TE Controller. For every BP
TE Controller. For every BP that is set in the BitString, and that that is set in the BitString, and that has one or more adjacencies in
has one or more adjacencies in the BIFT, a copy is made according to the BIFT, a copy is made according to the type of adjacencies for
the type of adjacencies for that BP in the BIFT. Before sending any that BP in the BIFT. Before sending any copy, the BFR clears all BPs
copy, the BFR clears all BPs in the BitString of the packet for which in the BitString of the packet for which the BFR has one or more
the BFR has one or more adjacencies in the BIFT, except when the adjacencies in the BIFT. Clearing these bits inhibits packets from
adjacency indicates "DoNotClear" (DNC, see Section 4.2.1). This is looping when the BitStrings erroneously includes a forwarding loop.
done to inhibit that packets can loop. Because DNC raises the risk When a forward_connected() adjacency has the "DoNotClear" (DNC) flag
of packets looping with inmakes it easier to set, then this BP is re-set for the packet copied to that adjacency.
See Section 4.2.1.
3.4. The Routing Underlay 3.4. The Routing Underlay
For forward_connected() adjacencies, BIER-TE is sending BIER packets For forward_connected() adjacencies, BIER-TE is sending BIER packets
to directly connected BIER-TE neighbors as L2 (unicasted) BIER to directly connected BIER-TE neighbors as L2 (unicasted) BIER
packets without requiring a routing underlay. For forward_routed() packets without requiring a routing underlay. For forward_routed()
adjacencies, BIER-TE forwarding encapsulates a copy of the BIER adjacencies, BIER-TE forwarding encapsulates a copy of the BIER
packet so that it can be delivered by the forwarding plane of the packet so that it can be delivered by the forwarding plane of the
routing underlay to the routable destination address indicated in the routing underlay to the routable destination address indicated in the
adjacency. See Section 4.2.2 for the adjacency definition. adjacency. See Section 4.2.2 for the adjacency definition.
BIER relies on the routing underlay to calculate paths towards BFERs BIER relies on the routing underlay to calculate paths towards BFERs
and derive next-hop BFR adjacencies for those paths. This commonly and derive next-hop BFR adjacencies for those paths. This commonly
relies on BIER specific extensions to the routing protocols of the relies on BIER specific extensions to the routing protocols of the
routing underlay but may also be established by a controller. In routing underlay but may also be established by a controller. In
BIER-TE, the next-hops of a packet are determined by the BitString BIER-TE, the next-hops of a packet are determined by the BitString
through the BIER-TE Controller established adjacencies on the BFR for through the BIER-TE Controller established adjacencies on the BFR for
the BPs of the BitString. There is thus no need for BFER specific the BPs of the BitString. There is thus no need for BFR specific
routing underlay extensions to forward BIER packets with BIER-TE routing underlay extensions to forward BIER packets with BIER-TE
semantics. semantics.
Encapsulation parameters can be provisioned by the BIER-TE controller Encapsulation parameters can be provisioned by the BIER-TE controller
into the forward_connected() or forward_routed() adjacencies directly into the forward_connected() or forward_routed() adjacencies directly
without relying on a routing underlay. without relying on a routing underlay.
If the BFR intends to support FRR for BIER-TE, then the BIER-TE If the BFR intends to support FRR for BIER-TE, then the BIER-TE
forwarding plane needs to receive fast adjacency up/down forwarding plane needs to receive fast adjacency up/down
notifications: Link up/down or neighbor up/down, e.g. from BFD. notifications: Link up/down or neighbor up/down, e.g. from BFD.
skipping to change at page 17, line 16 skipping to change at page 18, line 20
are out of scope of this document. are out of scope of this document.
Path steering is supported via the definition of a BitString. Path steering is supported via the definition of a BitString.
BitStrings used in BIER-TE are composed based on policy and resource BitStrings used in BIER-TE are composed based on policy and resource
management considerations. For example, when composing BIER-TE management considerations. For example, when composing BIER-TE
BitStrings, a Controller must take into account the resources BitStrings, a Controller must take into account the resources
available at each BFR and for each BP when it is providing available at each BFR and for each BP when it is providing
congestion-loss-free services such as Rate Controlled Service congestion-loss-free services such as Rate Controlled Service
Disciplines [RCSD94]. Resource availability could be provided for Disciplines [RCSD94]. Resource availability could be provided for
example via routing protocol information, but may also be obtained example via routing protocol information, but may also be obtained
via a BIER-TE control protocol such as Netconf or any other protocol via a BIER-TE control protocol such as NETCONF or any other protocol
commonly used by a Controller to understand the resources of the commonly used by a Controller to understand the resources of the
network it operates on. The resource usage of the BIER-TE traffic network it operates on. The resource usage of the BIER-TE traffic
admitted by the BIER-TE controller can be solely tracked on the BIER- admitted by the BIER-TE controller can be solely tracked on the BIER-
TE Controller based on local accounting as long as no TE Controller based on local accounting as long as no
forward_routed() adjacencies are used (see Section 4.2.1 for the forward_routed() adjacencies are used (see Section 4.2.1 for the
definition of forward_routed() adjacencies). When forward_routed() definition of forward_routed() adjacencies). When forward_routed()
adjacencies are used, the paths selected by the underlying routing adjacencies are used, the paths selected by the underlying routing
protocol need to be tracked as well. protocol need to be tracked as well.
Resource management has implications on the forwarding plane beyond Resource management has implications on the forwarding plane beyond
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traffic and potentially policing and/or rate-shaping mechanisms, traffic and potentially policing and/or rate-shaping mechanisms,
typically done via various forms of queuing. This level of resource typically done via various forms of queuing. This level of resource
control, while optional, is important in networks that wish to control, while optional, is important in networks that wish to
support congestion management policies to control or regulate the support congestion management policies to control or regulate the
offered traffic to deliver different levels of service and alleviate offered traffic to deliver different levels of service and alleviate
congestion problems, or those networks that wish to control latencies congestion problems, or those networks that wish to control latencies
experienced by specific traffic flows. experienced by specific traffic flows.
4. BIER-TE Forwarding 4. BIER-TE Forwarding
4.1. The Bit Index Forwarding Table (BIFT) 4.1. The BIER-TE Bit Index Forwarding Table (BIFT)
The Bit Index Forwarding Table (BIFT) exists in every BFR. For every The BIER-TE BIFT is the equivalent to the BIER BIFT for (non-TE)
sub-domain in use, it is a table indexed by SI:bit position and is BIER. It exists on every BFR running BIER-TE. For every BIER sub-
populated by the BIER-TE control plane. Each index can be empty or domain (SD) in use for BIER-TE, it is a table as shown shown in
contain a list of one or more adjacencies. Figure 4. That example BIFT assumes a BSL of 8 bit positions (BPs)
in the packets BitString. As in [RFC8279] this BSL is purely used
for the example and not a BIER/BIER-TE supported BSL (minimum BSL is
64).
Like BIER, BIER-TE can support multiple sub-domains, each with a A BIER-TE BIFT compares to a BIER BIFT as shown in [RFC8279] as
separate BIFT. follows.
In [RFC8279], Figure 2, indices into the BIFT are both SI:BitString In both BIER and BIER-TE, BIFT rows/entries are indexed in their
and BFR-id, where BitString is indicating a BP: BFR-id = SI * 2^BSL + respective BIER pseudocode ([RFC8279] Section 6.5) and BIER-TE
BP. As shown in Figure 4, in BIER-TE, only SI:BP are used as indices pseudocode (Section 4.4) by the BIFT-index derived from the packets
into a BIFT because they identify adjacencies and not BFR. SI, BSL and the one bit position of the packets BitString (BP)
addressing the BIFT row: BIFT-index = SI * BSL + BP - 1. BP within a
BitString are numbered from 1 to BSL, hence the - 1 offset when
converting to a BIFT-index. This document also uses the notion SI:BP
to indicate BIFT rows, [RFC8279] uses the equivalent notion
SI:BitString, where the BitString is filled with only the BP for the
BIFT row.
In BIER, each BIFT-index addresses one BFER by its BFR-id = BIFT-
index + 1 and is populated on each BFR with the next-hop "BFR
Neighbor" (BFR-NBR) towards that BFER.
In BIER-TE, each BIFT-index and therefore SI:BP indicates one or more
adjacencies between BFRs in the topology and is only populated with
those adjacencies forwarding entries on the BFR that is the upstream
for these adjacencies. The BIFT entry are empty on all other BFRs.
In BIER, each BIFT rows also requires a "Forwarding Bit Mask" (F-BM)
entry for BIER forwarding rules. In BIER-TE forwarding, F-BM is not
required, but can be used when implementing BIER-TE on forwarding
hardware derived from BIER forwarding, that must use F-BM. This is
discussed in the first BIER-TE forwarding pseudocode in Section 4.4.
------------------------------------------------------------------ ------------------------------------------------------------------
| Index: | Adjacencies: | | BIFT-index | | Adjacencies: |
| SI:bit position | <empty> or one or more per entry | | (SI:BP) |(FBM)| <empty> or one or more per entry |
================================================================== ==================================================================
| 0:1 | forward_connected(interface,neighbor{,DNC}) | | BIFT indices for Packets with SI=0 |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:2 | forward_connected(interface,neighbor{,DNC}) | | 0 (0:1) | ... | forward_connected(interface,neighbor{,DNC}) |
| | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:3 | local_decap({VRF}) | | 1 (0:2) | ... | forward_connected(interface,neighbor{,DNC}) |
| | ... | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:4 | forward_routed({VRF,}l3-neighbor) | | ... | ... | ... |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:5 | <empty> | | 4 (0:5) | ... | local_decap({VRF}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:6 | ECMP({adjacency1,...adjacencyN}, seed) | | 5 (0:6) | ... | forward_routed({VRF,}l3-neighbor) |
------------------------------------------------------------------ ------------------------------------------------------------------
... | 6 (0:7) | ... | <empty> |
| BitStringLength | ... |
------------------------------------------------------------------ ------------------------------------------------------------------
Bit Index Forwarding Table | 7 (0:8) | ... | ECMP((adjacency1,...adjacencyN){,seed}) |
-----------------------------------------------------------------
| BIFT indices for BitString/Packet with SI=1 |
------------------------------------------------------------------
| 9 (1:1) | | ... |
| ... |... | ... |
------------------------------------------------------------------
BIER-TE Bit Index Forwarding Table (BIFT)
Figure 4: BIFT adjacencies Figure 4: BIER-TE BIFT with different adjacencies
The BIFT is programmed into the data plane of BFRs by the BIER-TE The BIFT is configured for the BIER-TE data plane of a BFR by the
Controller and used to forward packets, according to the rules BIER-TE Controller through an appropriate protocol and data-model.
The BIFT is then used to forward packets, according to the rules
specified in the BIER-TE Forwarding Procedures. specified in the BIER-TE Forwarding Procedures.
Note that a BIFT index (SI:BP) may be populated in the BIFT of more Note that a BIFT index (SI:BP) may be populated in the BIFT of more
than one BFR. See Section 5.1.6 for an example of how a BIER-TE than one BFR to save BPs. See Section 5.1.6 for an example of how a
controller could assign BPs to (logical) adjacencies shared across BIER-TE controller could assign BPs to (logical) adjacencies shared
multiple BFRs, Section 5.1.3 for an example of assigning the same BP across multiple BFRs, Section 5.1.3 for an example of assigning the
to different adjacencies, and Section 5.1.9 for guidelines regarding same BP to different adjacencies, and Section 5.1.9 for general
re-use of BPs across different adjacencies. guidelines regarding re-use of BPs across different adjacencies.
{VRF} indicates the Virtual Routing and Forwarding context into which {VRF} indicates the Virtual Routing and Forwarding context into which
the BIER payload is to be delivered. This is optional and depends on the BIER payload is to be delivered. This is optional and depends on
the multicast flow overlay. the multicast flow overlay.
4.2. Adjacency Types 4.2. Adjacency Types
4.2.1. Forward Connected 4.2.1. Forward Connected
A "forward_connected" adjacency is towards a directly connected BFR A "forward_connected()" adjacency is towards a directly connected BFR
neighbor using an interface address of that BFR on the connecting neighbor using an interface address of that BFR on the connecting
interface. A forward_connected() adjacency does not route packets interface. A forward_connected() adjacency does not route packets
but only L2 forwards them to the neighbor. but only L2 forwards them to the neighbor.
Packets sent to an adjacency with "DoNotClear" (DNC) set in the BIFT Packets sent to an adjacency with "DoNotClear" (DNC) set in the BIFT
MUST NOT have the bit position for that adjacency cleared when the MUST NOT have the bit position for that adjacency cleared when the
BFR creates a copy for it. The bit position will still be cleared BFR creates a copy for it. The bit position will still be cleared
for copies of the packet made towards other adjacencies. This can be for copies of the packet made towards other adjacencies. This can be
used for example in ring topologies as explained in Section 5.1.6. used for example in ring topologies as explained in Section 5.1.6.
For protection against loops from misconfiguration (see For protection against loops from misconfiguration (see
Section 5.2.1), DNC is only permissible for forward_connected() Section 5.2.1), DNC is only permissible for forward_connected()
adjacencies. No need or benefit of DNC for other type of adjacencies adjacencies. No need or benefit of DNC for other type of adjacencies
was identified and their risk was not analyzed. was identified and their risk was not analyzed.
4.2.2. Forward Routed 4.2.2. Forward Routed
A "forward_routed" adjacency is an adjacency towards a BFR that uses A "forward_routed()" adjacency is an adjacency towards a BFR that
a (tunneling) encapsulation which will cause the packet to be uses a (tunneling) encapsulation which will cause the packet to be
forwarded by the routing underlay toward the adjacent BFR. This can forwarded by the routing underlay toward the adjacent BFR. This can
leverage any feasible encapsulation, such as MPLS or tunneling over leverage any feasible encapsulation, such as MPLS or tunneling over
IP/IPv6, as long as the BIER-TE packet can be identified as a IP/IPv6, as long as the BIER-TE packet can be identified as a
payload. This identification can either rely on the BIER/BIER-TE co- payload. This identification can either rely on the BIER/BIER-TE co-
existence mechanisms described in Section 4.3, or by explicit support existence mechanisms described in Section 4.3, or by explicit support
for a BIER-TE payload type in the tunneling encapsulation. for a BIER-TE payload type in the tunneling encapsulation.
"forward_routed" adjacencies are necessary to pass BIER-TE traffic forward_routed() adjacencies are necessary to pass BIER-TE traffic
across non BIER-TE capable routers or to minimize the number of across non BIER-TE capable routers or to minimize the number of
required BP by tunneling over (BIER-TE capable) routers on which required BP by tunneling over (BIER-TE capable) routers on which
neither replication nor path-steering is desired, or simply to neither replication nor path-steering is desired, or simply to
leverage path redundancy and FRR of the routing underlay towards the leverage path redundancy and FRR of the routing underlay towards the
next BFR. They may also be useful to a multi-subnet adjacent BFR to next BFR. They may also be useful to a multi-subnet adjacent BFR to
leverage the routing underlay ECMP independent of BIER-TE ECMP leverage the routing underlay ECMP independent of BIER-TE ECMP
(Section 4.2.3). (Section 4.2.3).
4.2.3. ECMP 4.2.3. ECMP
(non-TE) BIER ECMP is tied to the BIER BIFT processing semantic and (non-TE) BIER ECMP is tied to the BIER BIFT processing semantic and
are therefore not directly usable with BIER-TE. is therefore not directly usable with BIER-TE.
A BIER-TE "Equal Cost Multipath" (ECMP) adjacency has a list of two A BIER-TE "Equal Cost Multipath" (ECMP()) adjacency as shown in
or more non-ECMP adjacencies and a seed parameter. When a BIER-TE Figure 4 for BIFT-index 7 has a list of two or more non-ECMP
packet is copied onto such an ECMP adjacency, an implementation adjacencies as parameters and an optional seed parameter. When a
specific so-called hash function will select one out of the list's BIER-TE packet is copied onto such an ECMP() adjacency, an
adjacencies to which the packet is forwarded. This ECMP hash implementation specific so-called hash function will select one out
function MUST select the same adjacency from that list for all of the list's adjacencies to which the packet is forwarded. If the
packets with the same entropy parameter. The seed parameter allows packet's encapsulation contains an entropy field, the entropy field
to design hash functions that are easy to implement at high speed SHOULD be respected; two packets with the same value of the entropy
without running into polarization issues across multiple consecutive field SHOULD be sent on the same adjacency. The seed parameter
ECMP hops. See Section 5.1.7 for more explanations. allows to design hash functions that are easy to implement at high
speed without running into polarization issues across multiple
consecutive ECMP hops. See Section 5.1.7 for more explanations.
4.2.4. Local Decap(sulation) 4.2.4. Local Decap(sulation)
A "local_decap" adjacency passes a copy of the payload of the BIER-TE A "local_decap()" adjacency passes a copy of the payload of the BIER-
packet to the protocol ("NextProto") within the BFR (IPv4/IPv6, TE packet to the protocol ("NextProto") within the BFR (IPv4/IPv6,
Ethernet,...) responsible for that payload according to the packet Ethernet,...) responsible for that payload according to the packet
header fields. A local_decap() adjacency turns the BFR into a BFER header fields. A local_decap() adjacency turns the BFR into a BFER
for matching packets. Local_decap() adjacencies require the BFER to for matching packets. Local_decap() adjacencies require the BFER to
support routing or switching for NextProto to determine how to support routing or switching for NextProto to determine how to
further process the packet. further process the packet.
4.3. Encapsulation / Co-existence with BIER 4.3. Encapsulation / Co-existence with BIER
Specifications for BIER-TE encapsulation are outside the scope of Specifications for BIER-TE encapsulation are outside the scope of
this document. This section gives explanations and guidelines. this document. This section gives explanations and guidelines.
Like [RFC8279], handling of "Maximum Transmission Unit" (MTU)
limitations is outside the scope of this document and instead part of
the BIER-TE packet encapsulation and/or flow overlay. See for
example [RFC8296], Section 3. It applies equally to BIER-TE as it
does to BIER.
Because a BFR needs to interpret the BitString of a BIER-TE packet Because a BFR needs to interpret the BitString of a BIER-TE packet
differently from a (non-TE) BIER packet, it is necessary to differently from a (non-TE) BIER packet, it is necessary to
distinguish BIER from BIER-TE packets. In the BIER encapsulation distinguish BIER from BIER-TE packets. In the BIER encapsulation
[RFC8296], the BIFT-id field of the packet indicates the BIFT of the [RFC8296], the BIFT-id field of the packet indicates the BIFT of the
packet. BIER and BIER-TE can therefore be run simultaneously, when packet. BIER and BIER-TE can therefore be run simultaneously, when
the BIFT-id address space is shared across BIER BIFT and BIER-TE the BIFT-id address space is shared across BIER BIFT and BIER-TE
BIFT. Partitioning the BIFT-id address space is subject to BIER-TE/ BIFT. Partitioning the BIFT-id address space is subject to BIER-TE/
BIER control plane procedures. BIER control plane procedures.
When [RFC8296] is used for BIER with MPLS, BIFT-id address ranges can When [RFC8296] is used for BIER with MPLS, BIFT-id address ranges can
be dynamically allocated from MPLS label space only for the set of be dynamically allocated from MPLS label space only for the set of
actually used SD:BSL BIFT. This allows to also allocate non- actually used SD:BSL BIFT. This allows to also allocate non-
overlapping label ranges for BIFT-id that are to be used with BIER-TE overlapping label ranges for BIFT-id that are to be used with BIER-TE
BIFTs. BIFTs.
With MPLS, it is also possible to reuse the same SD space for both With MPLS, it is also possible to reuse the same SD space for both
BIER-TE and BIER, so that the same SD has both a BIER BIFT and BIER-TE and BIER, so that the same SD has both a BIER BIFT with a
corresponding range of BIFT-ids and a disjoint BIER-TE BIFT and non- corresponding range of BIFT-ids and disjoint BIER-TE BIFTs with a
overlapping range of BIFT-ids. non-overlapping range of BIFT-ids.
When a fixed mapping from BSL, SD, SI is used without specifically When a fixed mapping from BSL, SD and SI to BIFT-id is used which
distinguishing BIER and BIER-TE, such as proposed for non-MPLS does not explicitly partition the BIFT-id space between BIER and
forwarding with [RFC8296] in [I-D.ietf-bier-non-mpls-bift-encoding] BIER-TE, such as proposed for non-MPLS forwarding with [RFC8296]
revision 04, section 5., then it is necessary to allocate disjoint encapsulation in [I-D.ietf-bier-non-mpls-bift-encoding] revision 04,
SDs to BIER and BIER-TE BIFT so that both can be addressed by the section 5, then it is necessary to allocate disjoint SDs to BIER and
BIFT-ids. The encoding proposed in section 6. of the same document BIER-TE BIFTs so that both can be addressed by the BIFT-ids. The
does not statically encode BSL or SD into the BIFT-id, but allows for encoding proposed in section 6. of the same document does not
a mapping, and hence could provide for the same freedom as when MPLS statically encode BSL or SD into the BIFT-id, but allows for a
is being used (same or different SD for BIER/BIER-TE). mapping, and hence could provide for the same freedom as when MPLS is
being used (same or different SD for BIER/BIER-TE).
"forward_routed" requires an encapsulation that permits to direct forward_routed() requires an encapsulation that permits to direct
unicast encapsulated BIER-TE packets to a specific interface address unicast encapsulated BIER-TE packets to a specific interface address
on a target BFR. With MPLS encapsulation, this can simply be done on a target BFR. With MPLS encapsulation, this can simply be done
via a label stack with that addresses label as the top label - via a label stack with that addresses label as the top label -
followed by the label assigned to the (BSL,SD,SI) BitString. With followed by the label assigned to the (BSL,SD,SI) BitString. With
non-MPLS encapsulation, some form of IP encapsulation would be non-MPLS encapsulation, some form of IP encapsulation would be
required (for example IP/GRE). required (for example IP/GRE).
The encapsulation used for "forward_routed" adjacencies can equally The encapsulation used for forward_routed() adjacencies can equally
support existing advanced adjacency information such as "loose source support existing advanced adjacency information such as "loose source
routes" via e.g. MPLS label stacks or appropriate header extensions routes" via e.g. MPLS label stacks or appropriate header extensions
(e.g. for IPv6). (e.g. for IPv6).
4.4. BIER-TE Forwarding Pseudocode 4.4. BIER-TE Forwarding Pseudocode
The following pseudocode, Figure 5, for BIER-TE forwarding is based The following pseudocode, Figure 5, for BIER-TE forwarding is based
on the (non-TE) BIER forwarding pseudocode of [RFC8279], section 6.5 on the (non-TE) BIER forwarding pseudocode of [RFC8279], section 6.5
with one modification. with one modification.
skipping to change at page 22, line 23 skipping to change at page 24, line 25
PacketCopy is sent to that BFR-NBR ([1]). Likewise, the PacketCopy PacketCopy is sent to that BFR-NBR ([1]). Likewise, the PacketCopy
sent to a BFR-NBR must clear all bits in its BitString that are not sent to a BFR-NBR must clear all bits in its BitString that are not
routed across BFR-NBR. This protects against BIER replication on any routed across BFR-NBR. This protects against BIER replication on any
possible further BFR to create duplicates ([2]). possible further BFR to create duplicates ([2]).
To solve both [1] and [2] for BIER, the F-BM of each bit index needs To solve both [1] and [2] for BIER, the F-BM of each bit index needs
to have all bits set that this BFR wants to route across BFR-NBR. [2] to have all bits set that this BFR wants to route across BFR-NBR. [2]
clears all other bits in PacketCopy->BitString, and [1] clears those clears all other bits in PacketCopy->BitString, and [1] clears those
bits from Packet->BitString after the first PacketCopy. bits from Packet->BitString after the first PacketCopy.
In BIER-TE, a BFR-NBR is an adjacency, forward_connected, In BIER-TE, a BFR-NBR in this pseudocode is an adjacency,
forward_routed or local_decap. There is no need for [2] to suppress forward_connected(), forward_routed() or local_decap(). There is no
duplicates in the way BIER does because in general, different BP need for [2] to suppress duplicates in the way BIER does because in
would never have the same adjacency. If a BIER-TE controller general, different BP would never have the same adjacency. If a
actually finds some optimization in which this would be desirable, BIER-TE controller actually finds some optimization in which this
then the controller is also responsible to ensure that only one of would be desirable, then the controller is also responsible to ensure
those bits is set in any Packet->BitString, unless the controller that only one of those bits is set in any Packet->BitString, unless
explicitly wants for duplicates to be created. the controller explicitly wants for duplicates to be created.
For BIER-TE, F-BM is handled as follows: The following points describe how the forwarding bit mask (F-BM) for
each BP is configured in the BIFT and how this impacts the BitString
of the packet being processed with that BIFT:
1. The F-BM of all bits without an adjacency has all bits clear. 1. The F-BMs of all BIFT BPs without an adjacency have all their
This will cause [3] to skip further processing of such a bit. bits clear. This will cause [3] to skip further processing of
such a BP.
2. All bits with an adjacency (with DNC flag clear) have an F-BM 2. All BIFT BPs with an adjacency (with DNC flag clear) have an F-BM
that has only those bits set for which this BFR does not have an that has only those BPs set for which this BFR does not have an
adjacency. This causes [2] to clear all bits from adjacency. This causes [2] to clear all bits from
PacketCopy->BitString for which this BFR does have an adjacency. PacketCopy->BitString for which this BFR does have an adjacency.
3. [1] is not performed for BIER-TE. All bit clearing required by 3. [1] is not performed for BIER-TE. All bit clearing required by
BIER-TE is performed by [2]. BIER-TE is performed by [2].
This Forwarding Pseudocode can support the REQUIRED BIER-TE This Forwarding Pseudocode can support the required BIER-TE
forwarding functions (see Section 4.6), forward_connected, forwarding functions (see Section 4.6), forward_connected(),
forward_routed() and local decap, but not the RECOMMENDED functions forward_routed() and local_decap(), but not the recommended functions
DNC flag and multiple adjacencies per bit nor the OPTIONAL function, DNC flag and multiple adjacencies per bit nor the optional function,
ECMP adjacencies. The DNC flag cannot be supported when using only ECMP() adjacencies. The DNC flag cannot be supported when using only
[1] to mask bits. [1] to mask bits.
The modified and expanded Forwarding Pseudocode in Figure 6 specifies The modified and expanded Forwarding Pseudocode in Figure 6 specifies
how to support all BIER-TE forwarding functions (required, how to support all BIER-TE forwarding functions (required,
recommended and optional): recommended and optional):
* This pseudocode eliminates per-bit F-BM, therefore reducing the * This pseudocode eliminates per-bit F-BM, therefore reducing the
size of BIFT state by BitStringLength^2*SI and eliminating the size of BIFT state by BSL^2*SI and eliminating the need for per-
need for per-packet-copy masking operation except for adjacencies packet-copy BitString masking operations except for adjacencies
with the DNC flag set: with the DNC flag set:
- AdjacentBits[SI] are bits with a non-empty list of adjacencies. - AdjacentBits[SI] are bit positions with a non-empty list of
This can be computed whenever the BIER-TE Controller updates adjacencies in this BFR BIFT. This can be computed whenever
the adjacencies. the BIER-TE Controller updates (add/removes) adjacencies in the
BIFT.
- Only the AdjacentBits need to be examined in the loop for
packet copies.
- The packet's BitString is masked with those AdjacentBits before - The BFR needs to create packet copies for these adjacent bits
the loop to avoid doing this repeatedly for every PacketCopy. when they are set in the packets BitString. This set of bits
is calculated in PktAdjacentBits.
* The code loops over the adjacencies because there may be more than - All bit positions to which the BFR creates copies have to be
one adjacency for a bit. cleared in packet copies to avoid loops. This is done by
masking the BitString of the packet with ~AdjacentBits[SI].
When an adjacency has DNC set, this bit position is set again
only for the packet copy towards that bit position.
* When an adjacency has the DNC bit, the bit is set in the packet * BIFT entries may contain more than one adjacency in support of
copy (to save bits in rings for example). specific configurations such as Section 5.1.5. The code therefore
includes a loop over these adjacencies.
* The ECMP adjacency is shown. Its parameters are a * The ECMP() adjacency is shown. Its parameters are a seed and a
ListOfAdjacencies from which one is picked. ListOfAdjacencies from which one is picked.
* The forward_local, forward_routed, local_decap() adjacencies are * The forward_connected(), forward_routed(), local_decap()
shown with their parameters. adjacencies are shown with their parameters.
void ForwardBitMaskPacket_withTE (Packet) void ForwardBitMaskPacket_withTE (Packet)
{ {
SI=GetPacketSI(Packet); SI = GetPacketSI(Packet);
Offset=SI*BitStringLength; Offset = SI * BitStringLength;
// Set variable for looping across only adjacent bits // Determine adjacent bits in the Packets BitString
AdjacentBits = Packet->BitString & ~AdjacentBits[SI]; PktAdjacentBits = Packet->BitString & AdjacentBits[SI];
// Clear adjacent bits in Packet header to avoid loops // Clear adjacent bits in Packet header to avoid loops
Packet->BitString &= ~AdjacentBits[SI]; Packet->BitString &= ~AdjacentBits[SI];
for (Index = GetFirstBitPosition(AdjacentBits); Index ;
Index = GetNextBitPosition(AdjacentBits, Index)) { // Loop over PktAdjacentBits to create packet copies
foreach adjacency BIFT[Index+Offset] { for (Index = GetFirstBitPosition(PktAdjacentBits); Index ;
if(adjacency == ECMP(ListOfAdjacencies, seed) ) { Index = GetNextBitPosition(PktAdjacentBits, Index)) {
for adjacency in BIFT[Index+Offset]->Adjacencies {
if(adjacency.type == ECMP(ListOfAdjacencies,seed) ) {
I = ECMP_hash(sizeof(ListOfAdjacencies), I = ECMP_hash(sizeof(ListOfAdjacencies),
Packet->Entropy, seed); Packet->Entropy,seed);
adjacency = ListOfAdjacencies[I]; adjacency = ListOfAdjacencies[I];
} }
PacketCopy = Copy(Packet); PacketCopy = Copy(Packet);
switch(adjacency.type) { switch(adjacency.type) {
case forward_connected(interface,neighbor,DNC): case forward_connected(interface,neighbor,DNC):
if(adjacency.DNC) if(DNC)
PacketCopy->BitString |= 1<<(Index-1); PacketCopy->BitString |= 1<<(Index-1);
SendToL2Unicast(PacketCopy,interface,neighbor); SendToL2Unicast(PacketCopy,interface,neighbor);
case forward_routed({VRF},l3-neighbor): case forward_routed({VRF,}l3-neighbor):
SendToL3(PacketCopy,{VRF,}l3-neighbor); SendToL3(PacketCopy,{VRF,}l3-neighbor);
case local_decap({VRF},neighbor): case local_decap({VRF},neighbor):
DecapBierHeader(PacketCopy); DecapBierHeader(PacketCopy);
PassTo(PacketCopy,{VRF,}Packet->NextProto); PassTo(PacketCopy,{VRF,}Packet->NextProto);
} }
} }
} }
} }
Figure 6: Complete BIER-TE Forwarding Pseudocode for required, Figure 6: Complete BIER-TE Forwarding Pseudocode for required,
recommended and optional functions recommended and optional functions
4.5. Basic BIER-TE Forwarding Example 4.5. Basic BIER-TE Forwarding Example
[RFC Editor: remove this section.] [RFC Editor: remove this section.]
THIS SECTION TO BE REMOVED IN RFC BECAUSE IT WAS SUPERCEEDED BY THIS SECTION TO BE REMOVED IN RFC BECAUSE IT WAS SUPERSEDED BY
SECTION 1.1 EXAMPLE - UNLESS REVIEWERS CHIME IN AND EXPRESS DESIRE TO SECTION 1.1 EXAMPLE - IN CASE FINAL REVIES FIND A GOOD REASON TO KEEP
KEEP THIS ADDITIONAL EXAMPLE SECTION. ALVARO RETANA DID NOT MIND IT, BUT DOESN'T SEEM TO SHOW IMPORTANT NEW STUFF OVER INITIAL
ANOTHER EXAMPLE. EXAMPLES.
Step by step example of basic BIER-TE forwarding. This example does Step-by-step example of basic BIER-TE forwarding. This example does
not use ECMP or forward_routed() adjacencies nor does it try to not use ECMP() or forward_routed() adjacencies nor does it try to
minimize the number of required BitPositions for the topology. minimize the number of required BitPositions for the topology.
[BIER-TE Controller] [BIER-TE Controller]
/ | \ / | \
v v v v v v
. . . .
| p13 p1 | . | p13 p1 | .
+- BFIR2 --+ | . +- BFIR2 --+ | .
| . | p2 p6 | . LAN2 | . | p2 p6 | . LAN2
| . +-- BFR3 --+ . | | . +-- BFR3 --+ . |
skipping to change at page 26, line 36 skipping to change at page 28, line 36
BitString. The BIFT of BFIR2 has only p2 and p13 populated. Only p2 BitString. The BIFT of BFIR2 has only p2 and p13 populated. Only p2
is in the BitString and this is an adjacency towards BFR3. BFIR2 is in the BitString and this is an adjacency towards BFR3. BFIR2
therefore clears p2 in the BitString and sends a copy towards BFR2. therefore clears p2 in the BitString and sends a copy towards BFR2.
BFR3 sees a BitString of p5,p7,p8,p10,p11,p12. For those BPs, it has BFR3 sees a BitString of p5,p7,p8,p10,p11,p12. For those BPs, it has
only adjacencies for p7,p8. It creates a copy of the packet to BFER1 only adjacencies for p7,p8. It creates a copy of the packet to BFER1
(due to p7) and one to BFR4 (due to p8). It clears both p7 and p8 (due to p7) and one to BFR4 (due to p8). It clears both p7 and p8
before sending. before sending.
BFER1 sees a BitString of p5,p10,p11,p12. For those BPs, it only has BFER1 sees a BitString of p5,p10,p11,p12. For those BPs, it only has
an adjacency for p11. p11 is a "local_decap" adjacency installed by an adjacency for p11. p11 is a local_decap() adjacency installed by
the BIER-TE Controller to receive a copy of the BIER packet - dispose the BIER-TE Controller to receive a copy of the BIER packet - dispose
of the BIER header and pass the payload to IP multicast. IP of the BIER header and pass the payload to IP multicast. IP
multicast will then forward the packet out to LAN2 because it did multicast will then forward the packet out to LAN2 because it did
receive PIM or IGMP joins on LAN2 for the traffic. receive PIM or IGMP joins on LAN2 for the traffic.
Further processing of the packet in BFR4, BFR5 and BFER2 accordingly. Further processing of the packet in BFR4, BFR5 and BFER2 accordingly.
4.6. BFR Requirements for BIER-TE forwarding 4.6. BFR Requirements for BIER-TE forwarding
BFR MUST support to configure the BIFT of sub-domains so that they BFR that support BIER-TE and BIER MUST support configuration that
use BIER-TE forwarding rules instead of (non-TE) BIER forwarding enables BIER-TE instead of (non-TE) BIER forwarding rules for all
rules. Every BP in the BIFT MUST support to have zero or one BIFT of one or more BIER sub-domains. Every BP in a BIER-TE BIFT
adjacency. Forwarding MUST support the adjacency types MUST support to have zero or one adjacency. BIER-TE forwarding MUST
forward_connected() with clear DNC flag, forward_routed() and support the adjacency types forward_connected() with the DNC flag not
local_decap. As explained in Section 4.4, these REQUIRED BIER-TE set, forward_routed() and local_decap(). As explained in
forwarding functions can be implemented via the same Forwarding Section 4.4, these required BIER-TE forwarding functions can be
Pseudocode as BIER forwarding except for one modification (skipping implemented via the same Forwarding Pseudocode as BIER forwarding
one masking with F-BM). except for one modification (skipping one masking with F-BM).
BIER-TE forwarding SHOULD support forward_connected() adjacencies BIER-TE forwarding SHOULD support forward_connected() adjacencies
with a set DNC flag, as this is highly useful to save bits in rings with a set DNC flag, as this is highly useful to save bits in rings
(see Section 5.1.6). (see Section 5.1.6).
BIER-TE forwarding SHOULD support more than one adjacency on a bit. BIER-TE forwarding SHOULD support more than one adjacency on a bit.
This allows to save bits in hub&spoke scenarios (see Section 5.1.5). This allows to save bits in hub and spoke scenarios (see
Section 5.1.5).
BIER-TE forwarding MAY support ECMP adjacencies to save bits in ECMP BIER-TE forwarding MAY support ECMP() adjacencies to save bits in
scenarios, see Section 5.1.7 for an example. This is a MAY ECMP scenarios, see Section 5.1.7 for an example. This is an
requirement, because the deployment importance of ECMP adjacencies optional requirement, because for ECMP deployments using BIER-TE one
for BIER-TE is unclear as one can also leverage ECMP of the routing can also leverage ECMP of the routing underlay via forwarded_routed
underlay via forwarded_routed adjacencies and/or might prefer to have adjacencies and/or might prefer to have more explicit control of the
more explicit control of the path chosen via explicit BP/adjacencies path chosen via explicit BP/adjacencies for each ECMP path
for each ECMP path alternative. alternative.
5. BIER-TE Controller Operational Considerations 5. BIER-TE Controller Operational Considerations
5.1. Bit position Assignments 5.1. Bit Position Assignments
This section describes how the BIER-TE Controller can use the This section describes how the BIER-TE Controller can use the
different BIER-TE adjacency types to define the bit positions of a different BIER-TE adjacency types to define the bit positions of a
BIER-TE domain. BIER-TE domain.
Because the size of the BitString limits the size of the BIER-TE Because the size of the BitString limits the size of the BIER-TE
domain, many of the options described exist to support larger domain, many of the options described exist to support larger
topologies with fewer bit positions (4.1, 4.3, 4.4, 4.5, 4.6, 4.7, topologies with fewer bit positions.
4.8).
5.1.1. P2P Links 5.1.1. P2P Links
On a P2P link that connects two BFR, the same bit position can be On a P2P link that connects two BFRs, the same bit position can be
used on both BFR for the adjacency to the neighboring BFR. A P2P used on both BFRs for the adjacency to the neighboring BFR. A P2P
link requires therefore only one bit position. link requires therefore only one bit position.
5.1.2. BFER 5.1.2. BFER
Every non-Leaf BFER is given a unique bit position with a local_decap Every non-Leaf BFER is given a unique bit position with a
adjacency. local_decap() adjacency.
5.1.3. Leaf BFERs 5.1.3. Leaf BFERs
BFR1(P) BFR2(P) BFR1(P) BFR2(P) BFR1(P) BFR2(P) BFR1(P) BFR2(P)
| \ / | | | | \ / | | |
| X | | | | X | | |
| / \ | | | | / \ | | |
BFER1(PE) BFER2(PE) BFER1(PE)----BFER2(PE) BFER1(PE) BFER2(PE) BFER1(PE)----BFER2(PE)
^ U-turn link ^ U-turn link
Leaf BFER / Non-Leaf BFER / Leaf BFER / Non-Leaf BFER /
PE-router PE-router PE-router PE-router
Figure 10: Leaf vs. non-Leaf BFER Example Figure 10: Leaf vs. non-Leaf BFER Example
A leaf BFERs is one where incoming BIER-TE packets never need to be A leaf BFER is one where incoming BIER-TE packets never need to be
forwarded to another BFR but are only sent to the BFER to exit the forwarded to another BFR but are only sent to the BFER to exit the
BIER-TE domain. For example, in networks where Provider Edge (PE) BIER-TE domain. For example, in networks where Provider Edge (PE)
router are spokes connected to Provider (P) routers, those PEs are router are spokes connected to Provider (P) routers, those PEs are
Leaf BFERs unless there is a U-turn between two PEs. Leaf BFERs unless there is a U-turn between two PEs.
Consider how redundant disjoint traffic can reach BFER1/BFER2 in Consider how redundant disjoint traffic can reach BFER1/BFER2 in
Figure 10: When BFER1/BFER2 are Non-Leaf BFER as shown on the right Figure 10: When BFER1/BFER2 are Non-Leaf BFER as shown on the right-
hand side, one traffic copy would be forwarded to BFER1 from BFR1, hand side, one traffic copy would be forwarded to BFER1 from BFR1,
but the other one could only reach BFER1 via BFER2, which makes BFER2 but the other one could only reach BFER1 via BFER2, which makes BFER2
a non-Leaf BFER. Likewise BFER1 is a non-Leaf BFER when forwarding a non-Leaf BFER. Likewise, BFER1 is a non-Leaf BFER when forwarding
traffic to BFER2. Note that the BFERs in the left hand picture are traffic to BFER2. Note that the BFERs in the left-hand picture are
only guaranteed to be leaf-BFER by fitting routing configuration that only guaranteed to be leaf-BFER by fitting routing configuration that
prohibits transit traffic to pass through the BFERs, which is prohibits transit traffic to pass through the BFERs, which is
commonly applied in these topologies. commonly applied in these topologies.
All leaf-BFERs in a BIER-TE domain can share a single bit position. In most situations, leaf-BFER that are to be addressed via the same
This is possible because the bit position for the adjacency to reach BitString can share a single bit position for their local_decap()
the BFER can be used to distinguish whether or not packets should adjacency in that BitString and therefore save bit positions. On a
reach the BFER. non-leaf BFER, a received BIER-TE packet may only need to transit the
BFER or it may need to also be decapsulated. Whether or not to
decapsulate the packet therefore needs to be indicated by a unique
bit position populated only on the BIFT of this BFER with a
local_decap() adjacency. On a leaf-BFER, packets never need to pass
through; any packet received is therefore usually intended to be
decapsulated. This can be expressed by a single, shared bit position
that is populated with a local_decap() adjacency on all leaf-BFER
addressed by the BitString.
This optimization will not work if an upstream interface of the BFER The possible exception from this leaf-BFER bit position optimization
is using a bit position optimized as described in the following two can be cases where the bit position on the prior BIER-TE BFR (which
sections (LAN, Hub and Spoke). created the packet copy for the leaf-BFER in question) is populated
with multiple adjacencies as an optimization, such as in
Section 5.1.4 or Section 5.1.5. With either of these two
optimizations, the sender of the packet could only control explicitly
whether the packet was to be decapsulated on the leaf-BFER in
question, if the leaf-BFER has a unique bit position for its
local_decap() adjacency.
However, if the bit position is shared across leaf-BFER, and packets
are therefore decapsulated potentially unnecessarily, this may still
be appropriate if the decapsulated payload of the BIER-TE packet does
indicate whether or not the packet needs to be further processed/
received. This is typically true for example if the payload is IP
multicast because IP multicast on a BFER would know the membership
state of the IP multicast payload and be able to discard it if the
packet was delivered unnecessarily by the BIER-TE layer. If the
payload has no such membership indication, and the BFIR wants to have
explicit control about which BFER are to receive and decapsulate a
packet, then these two optimizations can not be used together with
shared bit positions optimization for leaf-BFER.
5.1.4. LANs 5.1.4. LANs
In a LAN, the adjacency to each neighboring BFR is given a unique bit In a LAN, the adjacency to each neighboring BFR is given a unique bit
position. The adjacency of this bit position is a position. The adjacency of this bit position is a
forward_connected() adjacency towards the BFR and this bit position forward_connected() adjacency towards the BFR and this bit position
is populated into the BIFT of all the other BFRs on that LAN. is populated into the BIFT of all the other BFRs on that LAN.
BFR1 BFR1
|p1 |p1
LAN1-+-+---+-----+ LAN1-+-+---+-----+
p3| p4| p2| p3| p4| p2|
BFR3 BFR4 BFR7 BFR3 BFR4 BFR7
Figure 11: LAN Example Figure 11: LAN Example
If Bandwidth on the LAN is not an issue and most BIER-TE traffic If Bandwidth on the LAN is not an issue and most BIER-TE traffic
should be copied to all neighbors on a LAN, then bit positions can be should be copied to all neighbors on a LAN, then bit positions can be
saved by assigning just a single bit position to the LAN and saved by assigning just a single bit position to the LAN and
populating the bit position of the BIFTs of each BFRs on the LAN with populating the bit position of the BIFTs of each BFRs on the LAN with
a list of forward_connected() adjacencies to all other neighbors on a list of forward_connected() adjacencies to all other neighbors on
the LAN. the LAN.
skipping to change at page 29, line 40 skipping to change at page 32, line 19
links can share the same bit position. The bit position on the hub's links can share the same bit position. The bit position on the hub's
BIFT is set up with a list of forward_connected() adjacencies, one BIFT is set up with a list of forward_connected() adjacencies, one
for each Spoke. for each Spoke.
This option is similar to the bit position optimization in LANs: This option is similar to the bit position optimization in LANs:
Redundantly connected spokes need their own bit positions, unless Redundantly connected spokes need their own bit positions, unless
they are themselves Leaf-BFER. they are themselves Leaf-BFER.
This type of optimized BP could be used for example when all traffic This type of optimized BP could be used for example when all traffic
is "broadcast" traffic (very dense receiver set) such as live-TV or is "broadcast" traffic (very dense receiver set) such as live-TV or
situation-awareness (SA). This BP optimization can then be used to many-to-many telemetry including situation-awareness (SA). This BP
explicitly steer different traffic flows across different ECMP paths optimization can then be used to explicitly steer different traffic
in Data-Center or broadband-aggregation networks with minimal use of flows across different ECMP paths in Data-Center or broadband-
BPs. aggregation networks with minimal use of BPs.
5.1.6. Rings 5.1.6. Rings
In L3 rings, instead of assigning a single bit position for every p2p In L3 rings, instead of assigning a single bit position for every p2p
link in the ring, it is possible to save bit positions by setting the link in the ring, it is possible to save bit positions by setting the
"DoNotClear" (DNC) flag on forward_connected() adjacencies. "DoNotClear" (DNC) flag on forward_connected() adjacencies.
For the rings shown in Figure 12, a single bit position will suffice For the rings shown in Figure 12, a single bit position will suffice
to forward traffic entering the ring at BFRa or BFRb all the way up to forward traffic entering the ring at BFRa or BFRb all the way up
to BFR1: to BFR1:
skipping to change at page 30, line 47 skipping to change at page 33, line 23
Both would be set up to stop rotating on the same link, e.g. L1. Both would be set up to stop rotating on the same link, e.g. L1.
When the ingress ring BFR creates the clockwise copy, it will clear When the ingress ring BFR creates the clockwise copy, it will clear
the counterclockwise bit position because the DNC bit only applies to the counterclockwise bit position because the DNC bit only applies to
the bit for which the replication is done. Likewise for the the bit for which the replication is done. Likewise for the
clockwise bit position for the counterclockwise copy. As a result, clockwise bit position for the counterclockwise copy. As a result,
the ring ingress BFR will send a copy in both directions, serving the ring ingress BFR will send a copy in both directions, serving
BFRs on either side of the ring up to L1. BFRs on either side of the ring up to L1.
5.1.7. Equal Cost MultiPath (ECMP) 5.1.7. Equal Cost MultiPath (ECMP)
The ECMP adjacency allows to use just one BP per link bundle between [RFC-Editor: A reviewer (Lars Eggert) noted that the infinite "to
two BFRs instead of one BP for each p2p member link of that link use" in the following sentence is not correct. The same was also
bundle. In Figure 13, one BP is used across L1,L2,L3. noted for several other similar instances. The following URL seems
to indicate though that this is a per-case decision, which seems
undefined: https://writingcenter.gmu.edu/guides/choosing-between-
infinitive-and-gerund-to-do-or-doing. What exactly should be done
about this ?].
An ECMP() adjacency allows to use just one BP to deliver packets to
one one of N adjacencies instead of one BP for each adjacency. In
the common example case Figure 13, a link-bundle of three links
L1,L2,L3 connects BFR1 and BFR2, and only one BP is used instead of
three BP to deliver packets from BFR1 to BFR2.
--L1----- --L1-----
BFR1 --L2----- BFR2 BFR1 --L2----- BFR2
--L3----- --L3-----
BIFT entry in BFR1: BIFT entry in BFR1:
------------------------------------------------------------------ ------------------------------------------------------------------
| Index | Adjacencies | | Index | Adjacencies |
================================================================== ==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR2), | | 0:6 | ECMP({forward_connected(L1, BFR2), |
skipping to change at page 31, line 31 skipping to change at page 34, line 31
================================================================== ==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR1), | | 0:6 | ECMP({forward_connected(L1, BFR1), |
| | forward_connected(L2, BFR1), | | | forward_connected(L2, BFR1), |
| | forward_connected(L3, BFR1)}, seed) | | | forward_connected(L3, BFR1)}, seed) |
------------------------------------------------------------------ ------------------------------------------------------------------
Figure 13: ECMP Example Figure 13: ECMP Example
This document does not standardize any ECMP algorithm because it is This document does not standardize any ECMP algorithm because it is
sufficient for implementations to document their freely chosen ECMP sufficient for implementations to document their freely chosen ECMP
algorithm. This allows the BIER-TE Controller to calculate ECMP algorithm. Figure 14 shows an example ECMP algorithm, and would
paths and seeds. Figure 14 shows an example ECMP algorithm: double as its documentation: A BIER-TE controller could determine
which adjacency is chosen based on the seed and adjacencies
parameters and the packet entropy.
forward(packet, ECMP(adj(0), adj(1),... adj(N-1), seed)): forward(packet, ECMP(adj(0), adj(1),... adj(N-1), seed)):
i = (packet(bier-header-entropy) XOR seed) % N i = (packet(bier-header-entropy) XOR seed) % N
forward packet to adj(i) forward packet to adj(i)
Figure 14: ECMP algorithm Example Figure 14: ECMP algorithm Example
In the following example, all traffic from BFR1 towards BFR10 is In the following example, all traffic from BFR1 towards BFR10 is
intended to be ECMP load split equally across the topology. This intended to be ECMP load split equally across the topology. This
example is not meant as a likely setup, but to illustrate that ECMP example is not meant as a likely setup, but to illustrate that ECMP
skipping to change at page 33, line 22 skipping to change at page 36, line 22
at all: BFR2 will only see traffic from BFR1 for which the ECMP hash at all: BFR2 will only see traffic from BFR1 for which the ECMP hash
in BFR1 selected the first adjacency in the list of 2 adjacencies in BFR1 selected the first adjacency in the list of 2 adjacencies
given as parameters to the ECMP. It is link L11-to-BFR2. BFR2 given as parameters to the ECMP. It is link L11-to-BFR2. BFR2
performs again ECMP with two adjacencies on that subset of traffic performs again ECMP with two adjacencies on that subset of traffic
using the same seed1, and will therefore again select the first of using the same seed1, and will therefore again select the first of
its two adjacencies: L21-to-BFR4. And therefore L22 and BFR5 sees no its two adjacencies: L21-to-BFR4. And therefore L22 and BFR5 sees no
traffic. Likewise for L31 and BFR6. traffic. Likewise for L31 and BFR6.
This issue in BFR2/BFR3 is called polarization. It results from the This issue in BFR2/BFR3 is called polarization. It results from the
re-use of the same hash function across multiple consecutive hops in re-use of the same hash function across multiple consecutive hops in
topologies like these. To resolve this issue, the ECMP adjacency on topologies like these. To resolve this issue, the ECMP() adjacency
BFR1 can be set up with a different seed2 than the ECMP adjacencies on BFR1 can be set up with a different seed2 than the ECMP()
on BFR2/BFR3. BFR2/BFR3 can use the same hash because packets will adjacencies on BFR2/BFR3. BFR2/BFR3 can use the same hash because
not sequentially pass across both of them. Therefore, they can also packets will not sequentially pass across both of them. Therefore,
use the same BP 0:7. they can also use the same BP 0:7.
Note that ECMP solutions outside of BIER often hide the seed by auto- Note that ECMP solutions outside of BIER often hide the seed by auto-
selecting it from local entropy such as unique local or next-hop selecting it from local entropy such as unique local or next-hop
identifiers. Allowing the BIER-TE Controller to explicitly set the identifiers. Allowing the BIER-TE Controller to explicitly set the
seed gives the ability for it to control same/different path seed gives the ability for it to control same/different path
selection across multiple consecutive ECMP hops. selection across multiple consecutive ECMP hops.
5.1.8. Forward Routed adjacencies 5.1.8. Forward Routed adjacencies
5.1.8.1. Reducing bit positions 5.1.8.1. Reducing bit positions
Forward_routed() adjacencies can reduce the number of bit positions Forward_routed() adjacencies can reduce the number of bit positions
required when the path steering requirement is not hop-by-hop required when the path steering requirement is not hop-by-hop
explicit path selection, but loose-hop selection. Forward_routed() explicit path selection, but loose-hop selection. Forward_routed()
adjacencies can also allow to operate BIER-TE across intermediate hop adjacencies can also allow to operate BIER-TE across intermediate hop
routers that do not support BIER-TE. routers that do not support BIER-TE.
............... ...............
...BFR1--... ...--L1-- BFR2... ...BFR1--... ...--L1-- BFR2...
... .Routers. ...--L2--/ ... .Routers. ...--L2--/
...BFR4--... ...------ BFR3... ...BFR4--... ...--L3-- BFR3...
... ...--L4--/ |
............... | ............... |
LO LO
Network Area 1 Network Area 1
Figure 16: Forward Routed Adjacencies Example Figure 16: Forward Routed Adjacencies Example
Assume the requirement in Figure 16 is to explicitly steer traffic Assume the requirement in Figure 16 is to explicitly steer traffic
flows that have arrived at BFR1 or BFR4 via a shortest path in the flows that have arrived at BFR1 or BFR4 via a path in the routing
routing underlay "Network Area 1" to one of the following three next underlay "Network Area 1" to one of the following three next
segments: (1) BFR2 via link L1, (2) BFR2 via link L2, or (3) via segments: (1) BFR2 via link L1, (2) BFR2 via link L2, or (3) via BFR3
BFR3. and then nor caring whether the packet is forwarded via L3 or L4.
To enable this, both BFR1 and BFR4 are set up with a forward_routed To enable this, both BFR1 and BFR4 are set up with a forward_routed
adjacency bit position towards an address of BFR2 on link L1, another adjacency bit position towards an address of BFR2 on link L1, another
forward_routed() bit position towards an address of BFR2 on link L2 forward_routed() bit position towards an address of BFR2 on link L2
and a third forward_routed() bit position towards a node address LO and a third forward_routed() bit position towards a node address LO
of BFR3. of BFR3.
5.1.8.2. Supporting nodes without BIER-TE 5.1.8.2. Supporting nodes without BIER-TE
Forward_routed() adjacencies also enable incremental deployment of Forward_routed() adjacencies also enable incremental deployment of
BIER-TE. Only the nodes through which BIER-TE traffic needs to be BIER-TE. Only the nodes through which BIER-TE traffic needs to be
steered - with or without replication - need to support BIER-TE. steered - with or without replication - need to support BIER-TE.
Where they are not directly connected to each other, forward_routed Where they are not directly connected to each other, forward_routed
adjacencies are used to pass over non BIER-TE enabled nodes. adjacencies are used to pass over non BIER-TE enabled nodes.
5.1.9. Reuse of bit positions (without DNC) 5.1.9. Reuse of bit positions (without DNC)
bit positions can be re-used across multiple BFR to minimize the Bit positions can be re-used across multiple BFRs to minimize the
number of BP needed. This happens when adjacencies on multiple BFR number of BP needed. This happens when adjacencies on multiple BFRs
use the DNC flag as described above, but it can also be done for non- use the DNC flag as described above, but it can also be done for non-
DNC adjacencies. This section only discusses this non-DNC case. DNC adjacencies. This section only discusses this non-DNC case.
Because BP are cleared when passing a BFR with an adjacency for that Because BP are cleared when passing a BFR with an adjacency for that
BP, reuse of BP across multiple BFR does not introduce any problems BP, reuse of BP across multiple BFRs does not introduce any problems
with duplicates or loops that do not also exist when every adjacency with duplicates or loops that do not also exist when every adjacency
has a unique BP. Instead, the challenge when reusing BP is whether has a unique BP. Instead, the challenge when reusing BP is whether
it allows to still achieve the desired Tree Engineering goals. it allows to still achieve the desired Tree Engineering goals.
BP cannot be reused across two BFR that would need to be passed BP cannot be reused across two BFRs that would need to be passed
sequentially for some path: The first BFR will clear the BP, so those sequentially for some path: The first BFR will clear the BP, so those
paths cannot be built. BP can be set across BFR that would (A) only paths cannot be built. BP can be set across BFR that would (A) only
occur across different paths or (B) across different branches of the occur across different paths or (B) across different branches of the
same tree. same tree.
An example of (A) was given in Figure 15, where BP 0:7, BP 0:8 and BP An example of (A) was given in Figure 15, where BP 0:7, BP 0:8 and BP
0:9 are each reused across multiple BFRs because a single packet/path 0:9 are each reused across multiple BFRs because a single packet/path
would never be able to reach more than one BFR sharing the same BP. would never be able to reach more than one BFR sharing the same BP.
Assume the example was changed: BFR1 has no ECMP adjacency for BP Assume the example was changed: BFR1 has no ECMP() adjacency for BP
0:6, but instead BP 0:5 with forward_connected() to BFR2 and BP 0:6 0:6, but instead BP 0:5 with forward_connected() to BFR2 and BP 0:6
with forward_connected() to BFR3. Packets with both BP 0:5 and BP with forward_connected() to BFR3. Packets with both BP 0:5 and BP
0:6 would now be able to reach both BFR2 and BFR3 and the still 0:6 would now be able to reach both BFR2 and BFR3 and the still
existing re-use of BP 0:7 between BFR2 and BFR3 is a case of (B) existing re-use of BP 0:7 between BFR2 and BFR3 is a case of (B)
where reuse of BP is perfect because it does not limit the set of where reuse of BP is perfect because it does not limit the set of
useful path choices: useful path choices:
If instead of reusing BP 0:7, BFR3 used a separate BP 0:10 for its If instead of reusing BP 0:7, BFR3 used a separate BP 0:10 for its
ECMP adjacency, no useful additional path steering options would be ECMP() adjacency, no useful additional path steering options would be
enabled. If duplicates at BFR10 where undesirable, this would be enabled. If duplicates at BFR10 where undesirable, this would be
done by not setting BP 0:5 and BP 0:6 for the same packet. If the done by not setting BP 0:5 and BP 0:6 for the same packet. If the
duplicates where desirable (e.g.: resilient transmission), the duplicates where desirable (e.g.: resilient transmission), the
additional BP 0:10 would also not render additional value. additional BP 0:10 would also not render additional value.
area1 area1
BFR1a BFR1b BFR1a BFR1b
/ \ / \
.................................... ....................................
. Core . . Core .
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* A hub with p2p connections to multiple non-leaf-BFER spokes can * A hub with p2p connections to multiple non-leaf-BFER spokes can
share one BP to all spokes if traffic can be flooded to all share one BP to all spokes if traffic can be flooded to all
spokes, e.g.: because of no bandwidth concerns or dense receiver spokes, e.g.: because of no bandwidth concerns or dense receiver
sets (Section 5.1.5). sets (Section 5.1.5).
* Rings of BFR can be built with just two BP (one for each * Rings of BFR can be built with just two BP (one for each
direction) except for BFR with multiple ring connections - similar direction) except for BFR with multiple ring connections - similar
to LANs (Section 5.1.6). to LANs (Section 5.1.6).
* ECMP adjacencies to N neighbors can replace N BP with 1 BP. * ECMP() adjacencies to N neighbors can replace N BP with 1 BP.
Multihop ECMP can avoid polarization through different seeds of Multihop ECMP can avoid polarization through different seeds of
the ECMP algorithm (Section 5.1.7). the ECMP algorithm (Section 5.1.7).
* Forward_routed() adjacencies allow to "tunnel" across non-BIER-TE * Forward_routed() adjacencies allow to "tunnel" across non-BIER-TE
capable routers and across BIER-TE capable routers where no capable routers and across BIER-TE capable routers where no
traffic-steering or replications are required (Section 5.1.8). traffic-steering or replications are required (Section 5.1.8).
* BP can generally be reused across a set of nodes where it can be * BP can generally be reused across a set of nodes where it can be
guaranteed that no path will ever need to traverse more than one guaranteed that no path will ever need to traverse more than one
node of the set. Depending on scenario, this may limit the node of the set. Depending on scenario, this may limit the
feasible path steering options (Section 5.1.9). feasible path steering options (Section 5.1.9).
Note that the described list of optimizations is not exhaustive. Note that the described list of optimizations is not exhaustive.
Especially when the set of required path steering choices is limited Especially when the set of required path steering choices is limited
and the set of possible subsets of BFERs that should be able to and the set of possible subsets of BFERs that should be able to
receive traffic is limited, further optimizations of BP are possible. receive traffic is limited, further optimizations of BP are possible.
The hub & spoke optimization is a simple example of such traffic The hub and spoke optimization is a simple example of such traffic
pattern dependent optimizations. pattern dependent optimizations.
5.2. Avoiding duplicates and loops 5.2. Avoiding duplicates and loops
5.2.1. Loops 5.2.1. Loops
Whenever BIER-TE creates a copy of a packet, the BitString of that Whenever BIER-TE creates a copy of a packet, the BitString of that
copy will have all bit positions cleared that are associated with copy will have all bit positions cleared that are associated with
adjacencies on the BFR. This inhibits looping of packets. The only adjacencies on the BFR. This inhibits looping of packets. The only
exception are adjacencies with DNC set. exception are adjacencies with DNC set.
v v v v
| | | |
L1 | L2 | L3 L1 | L2 | L3
skipping to change at page 40, line 9 skipping to change at page 42, line 49
In BIER-TE, BitStrings need to carry bits to indicate not only the In BIER-TE, BitStrings need to carry bits to indicate not only the
receiving BFER but also the intermediate hops/links across which the receiving BFER but also the intermediate hops/links across which the
packet must be sent. The maximum number of BFER that can be packet must be sent. The maximum number of BFER that can be
supported in a single BitString or BIFT:SI depends on the number of supported in a single BitString or BIFT:SI depends on the number of
bits necessary to represent the desired topology between them. bits necessary to represent the desired topology between them.
"Desired" topology because it depends on the physical topology, and "Desired" topology because it depends on the physical topology, and
on the desire of the operator to allow for explicit path steering on the desire of the operator to allow for explicit path steering
across every single hop (which requires more bits), or reducing the across every single hop (which requires more bits), or reducing the
number of required bits by exploiting optimizations such as unicast number of required bits by exploiting optimizations such as unicast
(forward_routed), ECMP or flood (DNC) over "uninteresting" sub-parts (forward_routed()), ECMP() or flood (DNC) over "uninteresting" sub-
of the topology - e.g. parts where different trees do not need to parts of the topology - e.g. parts where different trees do not need
take different paths due to path steering reasons. to take different paths due to path steering reasons.
The total number of bits to describe the topology vs. the number of The total number of bits to describe the topology vs. the number of
BFERs in a BIFT:SI can range widely based on the size of the topology BFERs in a BIFT:SI can range widely based on the size of the topology
and the amount of alternative paths in it. In a BIER-TE topology and the amount of alternative paths in it. In a BIER-TE topology
crafted by a BIER-TE expert, the higher the percentage of non-BFER crafted by a BIER-TE expert, the higher the percentage of non-BFER
bits, the higher the likelihood, that those topology bits are not bits, the higher the likelihood, that those topology bits are not
just BIER-TE overhead without additional benefit, but instead that just BIER-TE overhead without additional benefit, but instead that
they will allow to express desirable path steering alternatives. they will allow to express desirable path steering alternatives.
5.3.3. Assigning BFR-id with BIER-TE 5.3.3. Assigning BFR-id with BIER-TE
BIER-TE forwarding does not use the BFR-id, nor does it require for BIER-TE forwarding does not use the BFR-id, nor does it require for
the BFR-id field of the BIER header to be set to a particular value. the BFIR-id field of the BIER header to be set to a particular value.
However, other parts of a BIER-TE deployment may need a BFR-id, However, other parts of a BIER-TE deployment may need a BFR-id,
specifically overlay signaling, and in that case BFR need to also specifically multicast flow overlay signaling and multicast flow
have BFR-ids for BIER-TE SDs. overlay packet disposition, and in that case BFRs need to also have
BFR-ids for BIER-TE SDs.
For example, for BIER overlay signaling, BFIR need to have a BFR-id, For example, for BIER overlay signaling, BFIRs need to have a BFR-id,
because this BFIR BFR-id is carried in the BFR-id field of the BIER because this BFIR BFR-id is carried in the BFIR-id field of the BIER
header to indicate to the overlay signaling on the receiving BFER header to indicate to the overlay signaling on the receiving BFER
which BFIR originated the packet. which BFIR originated the packet.
In BIER, BFR-id = BSL * SI + BP, such that the SI and BP of a BFER In BIER, BFR-id = SI * BSL + BP, such that the SI and BP of a BFER
can be calculated from the BFR-id and vice versa. This also means can be calculated from the BFR-id and vice versa. This also means
that every BFR with a BFR-id has a reserved BP in an SI, even if that that every BFR with a BFR-id has a reserved BP in an SI, even if that
is not necessary for BIER forwarding, because the BFR may never be a is not necessary for BIER forwarding, because the BFR may never be a
BFER but only a BFIR. BFER but only a BFIR.
In BIER-TE, for a non-leaf BFER, there is usually a single BP for In BIER-TE, for a non-leaf BFER, there is usually a single BP for
that BFER with a local_decap() adjacency on the BFER. The BFR-id for that BFER with a local_decap() adjacency on the BFER. The BFR-id for
such a BFER can therefore equally be determined as in BIER: BFR-id = such a BFER can therefore be determined using the same procedure as
SI * BitStringLength + BP. in (non-TE) BIER: BFR-id = SI * BSL + BP.
As explained in Section 5.1.3, leaf BFERs do not need such a unique As explained in Section 5.1.3, leaf BFERs do not need such a unique
local_decap() adjacency, likewise, BFIR who are not also BFER may not local_decap() adjacency. Likewise, BFIRs that are not also BFERs may
have a unique local_decap() adjacency either. For all those BFIR and not have a unique local_decap() adjacency either. For all those
(leaf) BFER, the controller needs to determine unique BFR-ids that do BFIRs and (leaf) BFERs, the controller needs to determine unique BFR-
not collide with the BFR-ids derived from the non-leaf BFER ids that do not collide with the BFR-ids derived from the non-leaf
local_decap() BPs. BFER local_decap() BPs.
While this document defines no requirements how to allocate such BFR- While this document defines no requirements on how to allocate such
id, a simple option is to derive it from the (SI,BP) of an adjacency BFR-id, a simple option is to derive it from the (SI,BP) of an
that is unique to the BFR in question. For a BFIR this can be he adjacency that is unique to the BFR in question. For a BFIR this can
first adjacency only populated on this BFIR, for a leaf-BFER, this be the first adjacency only populated on this BFIR, for a leaf-BFER,
could be the first BP with an adjacency towards that BFER. this could be the first BP with an adjacency towards that BFER.
5.3.4. Mapping from BFR to BitStrings with BIER-TE 5.3.4. Mapping from BFR to BitStrings with BIER-TE
In BIER, applications of the flow overlay on a BFIR can calculate the In BIER, applications of the flow overlay on a BFIR can calculate the
(SI,BP) of a BFER from the BFR-id of the BFER and can therefore (SI,BP) of a BFER from the BFR-id of the BFER and can therefore
easily determine the BitStrings for a BIER packet to a set of BFER easily determine the BitStrings for a BIER packet to a set of BFERs
with known BFR-ids. with known BFR-ids.
In BIER-TE this mapping needs to be equally supported for flow In BIER-TE this mapping needs to be equally supported for flow
overlays. This section outlines two core options, based on how overlays. This section outlines two core options, based on what type
"complex" the Tree Engineering is that the BIER-TE controller of Tree Engineering the BIER-TE controller needs to performs for a
performs for a particular application. particular application.
"Independent branches": For a given flow overlay instance, the "Independent branches": For a given flow overlay instance, the
branches from a BFIR to every BFER are calculated by the BIER-TE branches from a BFIR to every BFER are calculated by the BIER-TE
controller to be independent of the branches to any other BFER. controller to be independent of the branches to any other BFER.
Shortest path trees are the most common examples of trees with Shortest path trees are the most common examples of trees with
independent branches. independent branches.
"Interdependent branches": When a BFER is added or deleted from a "Interdependent branches": When a BFER is added or deleted from a
particular distribution tree, the BIER-TE controller has to particular distribution tree, the BIER-TE controller has to
recalculate the branches to other BFER, because they may need to recalculate the branches to other BFER, because they may need to
change. Steiner trees are examples of interdependent branch trees. change. Steiner trees are examples of interdependent branch trees.
If "independent branches" are used, the BIER-TE Controller can signal If "independent branches" are used, the BIER-TE Controller can signal
to the BFIR flow overlay for every BFER an SI:BitString that to the BFIR flow overlay for every BFER an SI:BitString that
represents the branch to that BFER. The flow overlay on the BIFR can represents the branch to that BFER. The flow overlay on the BIFR can
then independently of the controller calculate the SI:BitString for then independently of the controller calculate the SI:BitString for
all desired BFER by OR'ing their BitStrings. This allows for flow all desired BFERs by OR'ing their BitStrings. This allows for flow
overlay applications to operate independently from the controller overlay applications to operate independently of the controller
whenever it needs to determine which subset of BFERs need to receive whenever it needs to determine which subset of BFERs need to receive
a particular packet. a particular packet.
If "interdependent branches" are required, the application would need If "interdependent branches" are required, the application would need
to inquire the SI:BitString for a given set of BFER whenever the set to inquire the SI:BitString for a given set of BFER whenever the set
changes. changes.
Note that in either case (unlike in BIER), the bits may need to Note that in either case (unlike in BIER), the bits may need to
change upon link/node failure/recovery, network expansion and network change upon link/node failure/recovery, network expansion and network
resource consumption by other traffic as part of traffic engineering resource consumption by other traffic as part of traffic engineering
goals (e.g.: re-optimization of lower priority traffic flows). goals (e.g.: re-optimization of lower priority traffic flows).
Interactions between such BFIR applications and the BIER-TE Interactions between such BFIR applications and the BIER-TE
Controller do therefore need to support dynamic updates to the Controller do therefore need to support dynamic updates to the
SI:BitStrings. SI:BitStrings.
Communications between BFIR flow overlay and BIER-TE controller Communications between the BFIR flow overlay and the BIER-TE
requires some way to identify BFER. If BFR-ids are used in the controller requires some way to identify the BFER. If BFR-ids are
deployment, as outlined in Section 5.3.3, then those are the natural used in the deployment, as outlined in Section 5.3.3, then those are
BFR identifier. If BFR-ids are not used, then any other unique the natural BFR identifier. If BFR-ids are not used, then any other
identifier, such as the BFR-prefix of the BFR as of [RFC8279] could unique identifier, such as the BFR-prefix of the BFR ([RFC8279])
be used. could be used.
5.3.5. Assigning BFR-ids for BIER-TE 5.3.5. Assigning BFR-ids for BIER-TE
It is not currently determined if a single sub-domain could or should It is not currently determined if a single sub-domain could or should
be allowed to forward both (non-TE) BIER and BIER-TE packets. If be allowed to forward both (non-TE) BIER and BIER-TE packets. If
this should be supported, there are two options: this should be supported, there are two options:
A. BIER and BIER-TE have different BFR-id in the same sub-domain. A. BIER and BIER-TE have different BFR-id in the same sub-domain.
This allows higher replication efficiency for BIER because their BFR- This allows higher replication efficiency for BIER because their BFR-
id can be assigned sequentially, while the BitStrings for BIER-TE id can be assigned sequentially, while the BitStrings for BIER-TE
will have also the additional bits for the topology. There is no will have also the additional bits for the topology. There is no
relationship between a BFR BIER BFR-id and BIER-TE BFR-id. relationship between a BFR BIER BFR-id and its BIER-TE BFR-id.
B. BIER and BIER-TE share the same BFR-id. The BFR-ids are assigned B. BIER and BIER-TE share the same BFR-id. The BFR-ids are assigned
as explained above for BIER-TE and simply reused for BIER. The as explained above for BIER-TE and simply reused for BIER. The
replication efficiency for BIER will be as low as that for BIER-TE in replication efficiency for BIER will be as low as that for BIER-TE in
this approach. this approach.
5.3.6. Example bit allocations 5.3.6. Example bit allocations
5.3.6.1. With BIER 5.3.6.1. With BIER
skipping to change at page 43, line 28 skipping to change at page 46, line 16
(most likely) have to receive all 4 copies of the BIER packet because (most likely) have to receive all 4 copies of the BIER packet because
there would be BFR-id for each of the 4 SIs in each of the areas. there would be BFR-id for each of the 4 SIs in each of the areas.
Only further towards each BFER would this duplication subside - when Only further towards each BFER would this duplication subside - when
each of the 4 trees runs out of branches. each of the 4 trees runs out of branches.
If BFR-ids are allocated intelligently, then all the BFER in an area If BFR-ids are allocated intelligently, then all the BFER in an area
would be given BFR-id with as few as possible different SIs. Each would be given BFR-id with as few as possible different SIs. Each
area would only have to forward one or two packets instead of 4. area would only have to forward one or two packets instead of 4.
Given how networks can grow over time, replication efficiency in an Given how networks can grow over time, replication efficiency in an
area will also easily go down over time when BFR-ids are network wide area will then also go down over time when BFR-ids are only allocated
allocated sequentially over time. An area that initially only has sequentially, network wide. An area that initially only has BFR-id
BFR-id in one SI might end up with many SIs over a longer period of in one SI might end up with many SIs over a longer period of growth.
growth. Allocating SIs to areas with initially sufficiently many Allocating SIs to areas with initially sufficiently many spare bits
spare bits for growths can help to alleviate this issue. Or renumber for growths can help to alleviate this issue. Or renumber BFERs
BFERs after network expansion. In this example one may consider to after network expansion. In this example one may consider to use 6
use 6 SIs and assign one to each area. SIs and assign one to each area.
This example shows that intelligent BFR-id allocation within at least This example shows that intelligent BFR-id allocation within at least
sub-domain 0 can even be helpful or even necessary in BIER. sub-domain 0 can even be helpful or even necessary in BIER.
5.3.6.2. With BIER-TE 5.3.6.2. With BIER-TE
In BIER-TE one needs to determine a subset of the physical topology In BIER-TE one needs to determine a subset of the physical topology
and attached BFERs so that the "desired" representation of this and attached BFERs so that the "desired" representation of this
topology and the BFER fit into a single BitString. This process topology and the BFER fit into a single BitString. This process
needs to be repeated until the whole topology is covered. needs to be repeated until the whole topology is covered.
Once bits/SIs are assigned to topology and BFERs, BFR-id is just a Once bits/SIs are assigned to topology and BFERs, BFR-id is just a
derived set of identifiers from the operator/BIER-TE Controller as derived set of identifiers from the operator/BIER-TE Controller as
explained above. explained above.
Every time that different sub-topologies have overlap, bits need to Every time that different sub-topologies have overlap, bits need to
be repeated across the BitStrings, increasing the overall amount of be repeated across the BitStrings, increasing the overall amount of
bits required across all BitString/SIs. In the worst case, random bits required across all BitString/SIs. In the worst case, one
subsets of BFERs are assigned to different SIs. This is much worse assigns random subsets of BFERs to different SIs. This will result
than in (non-TE) BIER because it not only reduces replication in an outcome much worse than in (non-TE) BIER: It maximizes the
efficiency with the same number of overall bits, but even further - amount of unnecessary topology overlap across SI and therefore
because more bits are required due to duplication of bits for reduces the number of BFER that can be reached across each individual
topology across multiple SIs. Intelligent BFER to SI assignment and SI. Intelligent BFER to SI assignment and selecting specific
selecting specific "desired" subtopologies can minimize this problem. "desired" subtopologies can minimize this problem.
To set up BIER-TE efficiently for the topology of Figure 20, the To set up BIER-TE efficiently for the topology of Figure 20, the
following bit allocation method can be used. This method can easily following bit allocation method can be used. This method can easily
be expanded to other, similarly structured larger topologies. be expanded to other, similarly structured larger topologies.
Each area is allocated one or more SIs depending on the number of Each area is allocated one or more SIs depending on the number of
future expected BFERs and number of bits required for the topology in future expected BFERs and number of bits required for the topology in
the area. In this example, 6 SIs, one per area. the area. In this example, 6 SIs, one per area.
In addition, we use 4 bits in each SI: bia, bib, bea, beb: (b)it In addition, we use 4 bits in each SI: bia, bib, bea, beb: (b)it
(i)ngress (a), (b)it (i)ngress (b), (b)it (e)gress (a), (b)it (i)ngress (a), (b)it (i)ngress (b), (b)it (e)gress (a), (b)it
(e)gress (b). These bits will be used to pass BIER packets from any (e)gress (b). These bits will be used to pass BIER packets from any
BFIR via any combination of ingress area a/b BFR and egress area a/b BFIR via any combination of ingress area a/b BFR and egress area a/b
BFR into a specific target area. These bits are then set up with the BFR into a specific target area. These bits are then set up with the
right forward_routed() adjacencies on the BFIR and area edge BFR: right forward_routed() adjacencies on the BFIR and area edge BFR:
On all BFIRs in an area j|j=2...6, bia in each BIFT:SI is populated On all BFIRs in an area j|j=1...6, bia in each BIFT:SI is populated
with the same forward_routed(BFRja), and bib with with the same forward_routed(BFRja), and bib with
forward_routed(BFRjb). On all area edge BFR, bea in forward_routed(BFRjb). On all area edge BFR, bea in
BIFT:SI=k|k=2...6 is populated with forward_routed(BFRka) and beb in BIFT:SI=k|k=1...6 is populated with forward_routed(BFRka) and beb in
BIFT:SI=k with forward_routed(BFRkb). For this setup we do not BIFT:SI=k with forward_routed(BFRkb).
consider area 1 because we assume the BIER-TE setup is just for
sending traffic from area 1 into area 2...6, for example bcause the
broadcast headends are in area 1 for an IPTV BIER-TE setup.
For BIER-TE forwarding of a packet to a subset of BFERs across all For BIER-TE forwarding of a packet to a subset of BFERs across all
areas, a BFIR would create at most 6 copies, with SI=1...SI=6, In areas, a BFIR would create at most 6 copies, with SI=1...SI=6, In
each packet, the bits indicate bits for topology and BFER in that each packet, the bits indicate bits for topology and BFER in that
topology plus the four bits to indicate whether to pass this packet topology plus the four bits to indicate whether to pass this packet
via the ingress area a or b border BFR and the egress area a or b via the ingress area a or b border BFR and the egress area a or b
border BFR, therefore allowing path steering for those two "unicast" border BFR, therefore allowing path steering for those two "unicast"
legs: 1) BFIR to ingress area edge and 2) core to egress area edge. legs: 1) BFIR to ingress area edge and 2) core to egress area edge.
Replication only happens inside the egress areas. For BFER in the Replication only happens inside the egress areas. For BFER in the
same area as in the BFIR, these four bits are not used. same area as in the BFIR, these four bits are not used.
5.3.7. Summary 5.3.7. Summary
BIER-TE can, like BIER, support multiple SIs within a sub-domain to BIER-TE can, like BIER, support multiple SIs within a sub-domain.
allow re-using the concept of BFR-id and therefore minimize BIER-TE This allows to apply the mapping BFR-id = SI * BSL + BP. This allows
specific functions in any possible BIER layer control plane used in to re-use the BIER architecture concept of BFR-id and therefore
conjunction with BIER-TE, flow overlay methods and BIER headers. minimize BIER-TE specific functions in possible BIER layer control
plane mechanisms with BIER-TE, including flow overlay methods and
BIER header fields.
The number of BFIR/BFER possible in a sub-domain is smaller than in The number of BFIR/BFER possible in a sub-domain is smaller than in
BIER because BIER-TE uses additional bits for topology. BIER because BIER-TE uses additional bits for topology.
Sub-domains (SDs) in BIER-TE can be used like in BIER to create more Sub-domains (SDs) in BIER-TE can be used like in BIER to create more
efficient replication to known subsets of BFERs. efficient replication to known subsets of BFERs.
Assigning bits for BFERs intelligently into the right SI is more Assigning bits for BFERs intelligently into the right SI is more
important in BIER-TE than in BIER because of replication efficiency important in BIER-TE than in BIER because of replication efficiency
and overall amount of bits required. and overall amount of bits required.
6. BIER-TE and Segment Routing 6. Security Considerations
SR aims to enable lightweight path steering via loose source routing.
Compared to its more heavy-weight predecessor RSVP-TE, SR does for
example not require per-path signaling to each of these hops.
BIER-TE supports the same design philosophy for multicast. Like in
SR, it relies on source-routing - via the definition of a BitString.
Like SR, it only requires to consider the "hops" on which either
replication has to happen, or across which the traffic should be
steered (even without replication). Any other hops can be skipped
via the use of routed adjacencies.
BIER-TE bit position (BP) can be understood as the BIER-TE equivalent
of "forwarding segments" in SR, but they have a different scope than
SR forwarding segments. Whereas forwarding segments in SR are global
or local, BPs in BIER-TE have a scope that is the group of BFR(s)
that have adjacencies for this BP in their BIFT. This can be called
"adjacency" scoped forwarding segments.
Adjacency scope could be global, but then every BFR would need an
adjacency for this BP, for example a forward_routed() adjacency with
encapsulation to the global SR SID of the destination. Such a BP
would always result in ingress replication though (as in [RFC7988]).
The first BFR encountering this BP would directly replicate to it.
Only by using non-global adjacency scope for BPs can traffic be
steered and replicated on non-ingress BFR.
SR can naturally be combined with BIER-TE and help to optimize it.
For example, instead of defining bit positions for non-replicating
hops, it is equally possible to use segment routing encapsulations
(e.g. SR-MPLS label stacks) for the encapsulation of
"forward_routed" adjacencies.
Note that (non-TE) BIER itself can also be seen to be similar to SR.
BIER BPs act as global destination Node-SIDs and the BIER BitString
is simply a highly optimized mechanism to indicate multiple such SIDs
and let the network take care of effectively replicating the packet
hop-by-hop to each destination Node-SID. What BIER does not allow is
to indicate intermediate hops, or in terms of SR the ability to
indicate a sequence of SID to reach the destination. This is what
BIER-TE and its adjacency scoped BP enables.
7. Security Considerations
If [RFC8296] is used, BIER-TE shares its security considerations. If [RFC8296] is used, BIER-TE shares its security considerations.
BIER-TE shares the security considerations of BIER, [RFC8279], with BIER-TE shares the security considerations of BIER, [RFC8279], with
the following overriding or additional considerations. the following overriding or additional considerations.
BIER-TE forwarding explicitly supports unicast "tunneling" of BIER
packets via forward_routed() adjacencies. The BIER domain security
model is based on a subset of interfaces on a BFR that connect to
other BFRs of the same BIER domain. For BIER-TE, this security model
equally applies to such unicast "tunneled" BIER packets. This does
not only include the need to filter received unicast "tunneled" BIER
packets to prohibit injection of such "tunneled" BIER packets from
outside the BIER domain, but also prohibiting forward_routed()
adjacencies to leak BIER packets from the BIER domain. It SHOULD be
possible to configure interfaces to be part of a BIER domain solely
for sending and receiving of unicast "tunneled" BIER packets even if
the interface can not send/receive BIER encapsulated packets.
In BIER, the standardized methods for the routing underlays are IGPs In BIER, the standardized methods for the routing underlays are IGPs
with extensions to distribute BFR-ids and BFR-prefixes. [RFC8401] with extensions to distribute BFR-ids and BFR-prefixes. [RFC8401]
specifies the extensions for IS-IS and [RFC8444] specifies the specifies the extensions for IS-IS and [RFC8444] specifies the
extensions for OSPF. Attacking the protocols for the BIER routing extensions for OSPF. Attacking the protocols for the BIER routing
underlay or (non-TE) BIER layer control plane, or impairment of any underlay or (non-TE) BIER layer control plane, or impairment of any
BFR in a domain may lead to successful attacks against the results of BFR in a domain may lead to successful attacks against the results of
the routing protocol, enabling DoS attacks against paths or the the routing protocol, enabling DoS attacks against paths or the
addressing (BFR-id, BFR-prefixes) used by BIER. addressing (BFR-id, BFR-prefixes) used by BIER.
The reference model for the BIER-TE layer control plane is a BIER-TE The reference model for the BIER-TE layer control plane is a BIER-TE
controller. When such a controller is used, impairment of individual controller. When such a controller is used, impairment of an
BFR in a domain causes no impairment of the BIER-TE control plane on individual BFR in a domain causes no impairment of the BIER-TE
other BFR. If a routing protocol is used to support forward_routed() control plane on other BFRs. If a routing protocol is used to
adjacencies, then this is still an attack vector as in BIER, but only support forward_routed() adjacencies, then this is still an attack
for BIER-TE forward_routed() adjacencies, and not other adjacencies. vector as in BIER, but only for BIER-TE forward_routed() adjacencies,
and not other adjacencies.
Whereas IGP routing protocols are most often not well secured through Whereas IGP routing protocols are most often not well secured through
cryptographic authentication and confidentiality, communications cryptographic authentication and confidentiality, communications
between controllers and routers such as those to be considered for between controllers and routers such as those to be considered for
the BIER-TE controller/control-plane can be and are much more the BIER-TE controller/control-plane can be and are much more
commonly secured with those security properties, for example by using commonly secured with those security properties, for example by using
Secure SHell (SSH), [RFC4253] for NetConf ([RFC6241]), or via Secure SHell (SSH), [RFC4253] for NETCONF ([RFC6242]), or via
Transport Layer Security (TLS), such as [RFC8253] for PCEP, Transport Layer Security (TLS), such as [RFC8253] for PCEP,
[RFC5440], or [RFC7589] for NetConf. BIER-TE controllers SHOULD use [RFC5440], or [RFC7589] for NETCONF. BIER-TE controllers SHOULD use
security equal to or better than these mechanisms. security equal to or better than these mechanisms.
For additional, BIER-TE independent security considerations for the When any of these security mechanisms/protocols are used for
use of a central BIER-TE controller, the security section of the communications between a BIER-TE controller and BFRs, their security
protocols and security options in the previous paragraph apply. In considerations apply to BIER-TE. In addition, the security
addition, the security considerations of [RFC4655] apply. considerations of PCE, [RFC4655] apply.
The most important attack vector in BIER-TE is misconfiguration, The most important attack vector in BIER-TE is misconfiguration,
either on the BFR themselves or via the BIER-TE controller. either on the BFR themselves or via the BIER-TE controller.
Forwarding entries with DNC could be set up to create persistent Forwarding entries with DNC could be set up to create persistent
loops, in which packets only expire because of TTL. To minimize the loops, in which packets only expire because of TTL. To minimize the
impact of such attacks (or more likely unintentional misconfiguration impact of such attacks (or more likely unintentional misconfiguration
by operators and/or bad BIER-TE controller software), the BIER-TE by operators and/or bad BIER-TE controller software), the BIER-TE
forwarding rules are defined to be as strict in clearing bits as forwarding rules are defined to be as strict in clearing bits as
possible. The clearing of all bits with an adjacency on a BFR possible. The clearing of all bits with an adjacency on a BFR
prohibits that a looping packet creates additional packet prohibits that a looping packet creates additional packet
skipping to change at page 47, line 28 skipping to change at page 49, line 39
network's life-cycle, such as in embedded networks or in network's life-cycle, such as in embedded networks or in
manufacturing networks during e.g. plant reworking/repairs. In these manufacturing networks during e.g. plant reworking/repairs. In these
type of deployments, configuration changes could be locked out when type of deployments, configuration changes could be locked out when
the network is in production state and could only be (re-)enabled the network is in production state and could only be (re-)enabled
through reverting the network/installation into non-production state. through reverting the network/installation into non-production state.
Such security designs would not only allow to provide additional Such security designs would not only allow to provide additional
layers of protection against configuration attacks, but would layers of protection against configuration attacks, but would
foremost protect the active production process from such foremost protect the active production process from such
configuration attacks. configuration attacks.
8. IANA Considerations 7. IANA Considerations
This document requests no action by IANA. This document requests no action by IANA.
9. Acknowledgements 8. Acknowledgements
The authors would like to thank Greg Shepherd, Ijsbrand Wijnands, The authors would like to thank Greg Shepherd, Ijsbrand Wijnands,
Neale Ranns, Dirk Trossen, Sandy Zheng, Lou Berger, Jeffrey Zhang, Neale Ranns, Dirk Trossen, Sandy Zheng, Lou Berger, Jeffrey Zhang,
Alvaro Retana and Wolfgang Braun for their reviews and suggestions. Carsten Borman and Wolfgang Braun for their reviews and suggestions.
10. Change log [RFC Editor: Please remove] Special thanks to Xuesong Geng for shepherding the document and for
IESG review/suggestions by Alvaro Retana (responsible AD/RTG),
Benjamin Kaduk (SEC), Tommy Pauly (TSV), Zaheduzzaman Sarker (TSV),
Eric Vyncke (INT), Martin Vigoureux (RTG), Robert Wilton (OPS), Eric
Kline (INT), Lars Eggert (GEN), Roman Danyliv (SEC), Ines Robles
(RTGDIR), Robert Sparks (Gen-ART), Yingzhen Qu (RTGdir), Martin Duke
(TSV).
9. Change log [RFC Editor: Please remove]
draft-ietf-bier-te-arch: draft-ietf-bier-te-arch:
12:
AD review Alvaro Retana.
Various textual/editorial nits including adding () to all
instances of forwarding adjacency name instances.
3.1 Added new paragraph outlining possible use of BGP as RR in
BIER-TE controller as core of multicast flow overlay component of
BIER-TE.
3.2 added xref's to relevant sections to the listed control plane
points.
4.1 rewrote paragraphs of 4.1 leading up to Figure 4. to eliminate
any confusion in how the BIFT work and how it compares to the
notions in rfc8279, as well as better linking it to the
Pseudocode.
Moved SR section into appendix.
TSV review Martin Duke.
Text/editorial nits.
4.4 improved text describing handling of F-BM.
RTGdir review Yingzhen Qu.
Various text/editorial nits.
Added notion that BitStrings represent loop free tree for packet
to abstract and intro.
Various text nit and editorial improvements.
Fixed some BFR-id field -> BFIR-id field mistakes.
Capitalized NETCONF/RESTCONF/YANG, added RFC references.
Improved Figure 16 with explicitly two links into BFR3 and
explanatory text.
Gen-ART review Robert Sparks.
Various textual nits, editorial improvements.
3.2 Introduced terms "BIER-TE topology control" and "BIER-TE tree
control" for the two functional components of the control plane.
3.2.1 - 3.2 change introduces the open RFC-editor issue of
appropriate xrfs (to be resolved by RFC-editor).
3.3 Rewrote last paragraph to better describe loop prevention
through clearing of bits in BitString.
4.1 Fixed up text/formula describing mapping between bfr-id, SI:BP
and SI,BSL and BP. Fix offset bug.
5.3.6.2 Improved description paragraph explaining overlap of
topology for different SI.
5.3.7 Improved first summary paragraph.
7. Rephrased applicability statement of control plane protocol
security considerations to BIER-TE security.
RTGDIR review Ines Robles.
Fixed up adjacencies in Example 2 and explanation text to be
explicit about which BFR not only passes, but also receives the
packet.
7. (security considerations). Added paragraph about
forward_routed() and prohibiting BIER packet leaking in/out of
domain.
IESG review Roman Danyliv (SEC).
Several textual/sentence nits/editorials.
IESG review Lars Eggert (GEN).
Various good editorial word fixed.
Pointer to non-false-positive bloom filter work that looks like it
happened after our IETF discussions documented in this doc, so
will not add it to doc, but here is URL for folks interested:
https://ieeexplore.ieee.org/document/8486415.
Did not change "native" to a different word for inclusivity
because of my worry there is no estavblished single replacement
word, making reading/searching/understanding more difficult.
IESG review Martin Vigeureux (RTG).
Added back reference to RFC8402. Textual fixes.
IESG review Eric Kline (INT).
2.1 Fixed typo in BFR* explanations.
4.3 Added explanatio about MTU handling.
IESG review Eric Vyncke (INT).
Fixed up initial text to introduce various abbreviations.
2.4 refined wording to "with the _intent_ to easily build common
forwarding planes...".
4.2.3 refined text about entropy in ECMP - now taken text from
rfc8279.
IESG review Zaheduzzaman Sarker (TSV).
5.1.7 Refined text explaining documentation of ECMP algorithm.
5.3.6.2. fixed range of areas/SI over which to build the example
large network BPs - removed explanation of the large network shown
to be only used for sources in area 1 (IPTV), because it was a
stale explanation.
IESG review Ben Kaduk (round 2):
4.4 Advanced pseudocode still had one wrong "~". Root cause seems
to have been day 0 problem in pseudocode written for -01, "~" was
inserted in the wrong one of two code lines. Also enhanced
textual description and comments in pseudocode, changed variable
name AdjacentBits to PktAdjacentBits to avoid confusion with
AdjacentBits[SI].
5.1.3 Rewrote last two paragraphs explaining the sharing of bit
positions for lead-BFER hopefully better. Also detailled how it
interacts with other optimizations and the type of payload BIER-TE
packets may carry.
4.4 (from Carsten Borman) changed spacing in pseudocode to be
consistent. Fixed {VRF}, clarified pseudocode object syntax,
typos.
11: IESG review Ben Kaduk, summary: 11: IESG review Ben Kaduk, summary:
One discuss for bug in pseudocode. turned out to be one cahrcter One discuss for bug in pseudocode. turned out to be one cahrcter
typo. typo.
Added (non-TE) prefix in places where BIER by itsels had to be Added (non-TE) prefix in places where BIER by itsels had to be
better disambiguated. better disambiguated.
enhanced text for hub-and-spoke to indicate we're only talking enhanced text for hub-and-spoke to indicate we're only talking
about hub to spoke traffic. about hub to spoke traffic.
skipping to change at page 55, line 36 skipping to change at page 60, line 50
BIER forwarding. Removed MyBitsOfInterest (was pure BIER forwarding. Removed MyBitsOfInterest (was pure
optimization). optimization).
- Added captions to pictures. - Added captions to pictures.
- Part of review feedback from Sandy (Zhang Zheng) integrated. - Part of review feedback from Sandy (Zhang Zheng) integrated.
00: Changed target state to experimental (WG conclusion), updated 00: Changed target state to experimental (WG conclusion), updated
references, mod auth association. references, mod auth association.
- Source now on http://www.github.com/toerless/bier-te-arch - Source now on https://www.github.com/toerless/bier-te-arch
- Please open issues on the github for change/improvement requests - Please open issues on the github for change/improvement requests
to the document - in addition to posting them on the list to the document - in addition to posting them on the list
(bier@ietf.). Thanks!. (bier@ietf.). Thanks!.
draft-eckert-bier-te-arch: draft-eckert-bier-te-arch:
06: Added overview of forwarding differences between BIER, BIER- 06: Added overview of forwarding differences between BIER, BIER-
TE. TE.
05: Author affiliation change only. 05: Author affiliation change only.
skipping to change at page 57, line 20 skipping to change at page 62, line 34
all ring nodes. all ring nodes.
01: Fixed BFIR -> BFER for section 4.3. 01: Fixed BFIR -> BFER for section 4.3.
01: Added explanation of SI, difference to BIER ECMP, 01: Added explanation of SI, difference to BIER ECMP,
consideration for Segment Routing, unicast FRR, considerations for consideration for Segment Routing, unicast FRR, considerations for
encapsulation, explanations of BIER-TE Controller and CLI. encapsulation, explanations of BIER-TE Controller and CLI.
00: Initial version. 00: Initial version.
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
skipping to change at page 57, line 45 skipping to change at page 63, line 11
Explicit Replication (BIER)", RFC 8279, Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017, DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>. <https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., [RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non- for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>. 2018, <https://www.rfc-editor.org/info/rfc8296>.
11.2. Informative References 10.2. Informative References
[Bloom70] Bloom, B. H., "Space/time trade-offs in hash coding with [Bloom70] Bloom, B. H., "Space/time trade-offs in hash coding with
allowable errors", Comm. ACM 13(7):422-6, July 1970, allowable errors", Comm. ACM 13(7):422-6, July 1970,
<http://gnunet.org/papers/p422-bloom.pdf>. <https://dl.acm.org/doi/10.1145/362686.362692>.
[I-D.eckert-bier-te-frr] [I-D.eckert-bier-te-frr]
Eckert, T., Cauchie, G., Braun, W., and M. Menth, Eckert, T., Cauchie, G., Braun, W., and M. Menth,
"Protection Methods for BIER-TE", Work in Progress, "Protection Methods for BIER-TE", Work in Progress,
Internet-Draft, draft-eckert-bier-te-frr-03, 5 March 2018, Internet-Draft, draft-eckert-bier-te-frr-03, 5 March 2018,
<https://www.ietf.org/archive/id/draft-eckert-bier-te-frr- <https://www.ietf.org/archive/id/draft-eckert-bier-te-frr-
03.txt>. 03.txt>.
[I-D.ietf-bier-multicast-http-response] [I-D.ietf-bier-multicast-http-response]
Trossen, D., Rahman, A., Wang, C., and T. Eckert, Trossen, D., Rahman, A., Wang, C., and T. Eckert,
skipping to change at page 59, line 16 skipping to change at page 64, line 34
<https://ieeexplore.ieee.org/document/7511036>. <https://ieeexplore.ieee.org/document/7511036>.
[RCSD94] Zhang, H. and D. Domenico, "Rate-Controlled Service [RCSD94] Zhang, H. and D. Domenico, "Rate-Controlled Service
Disciplines", Journal of High-Speed Networks, 1994, May Disciplines", Journal of High-Speed Networks, 1994, May
1994, <https://dl.acm.org/doi/10.5555/2692227.2692232>. 1994, <https://dl.acm.org/doi/10.5555/2692227.2692232>.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>. January 2006, <https://www.rfc-editor.org/info/rfc4253>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655, Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006, DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>. <https://www.rfc-editor.org/info/rfc4655>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440, Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009, DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>. <https://www.rfc-editor.org/info/rfc5440>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>. <https://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the [RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
NETCONF Protocol over Transport Layer Security (TLS) with NETCONF Protocol over Transport Layer Security (TLS) with
Mutual X.509 Authentication", RFC 7589, Mutual X.509 Authentication", RFC 7589,
DOI 10.17487/RFC7589, June 2015, DOI 10.17487/RFC7589, June 2015,
<https://www.rfc-editor.org/info/rfc7589>. <https://www.rfc-editor.org/info/rfc7589>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752, Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016, DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>. <https://www.rfc-editor.org/info/rfc7752>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7988] Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress [RFC7988] Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
Replication Tunnels in Multicast VPN", RFC 7988, Replication Tunnels in Multicast VPN", RFC 7988,
DOI 10.17487/RFC7988, October 2016, DOI 10.17487/RFC7988, October 2016,
<https://www.rfc-editor.org/info/rfc7988>. <https://www.rfc-editor.org/info/rfc7988>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the "PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)", Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017, RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>. <https://www.rfc-editor.org/info/rfc8253>.
[RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N., [RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N.,
Ananthakrishnan, H., and X. Liu, "A YANG Data Model for Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
2018, <https://www.rfc-editor.org/info/rfc8345>. 2018, <https://www.rfc-editor.org/info/rfc8345>.
[RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z. [RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
Zhang, "Bit Index Explicit Replication (BIER) Support via Zhang, "Bit Index Explicit Replication (BIER) Support via
IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018, IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
<https://www.rfc-editor.org/info/rfc8401>. <https://www.rfc-editor.org/info/rfc8401>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A., [RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2 Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
Extensions for Bit Index Explicit Replication (BIER)", Extensions for Bit Index Explicit Replication (BIER)",
RFC 8444, DOI 10.17487/RFC8444, November 2018, RFC 8444, DOI 10.17487/RFC8444, November 2018,
<https://www.rfc-editor.org/info/rfc8444>. <https://www.rfc-editor.org/info/rfc8444>.
[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
Appendix A. BIER-TE and Segment Routing
SR (xref target="RFC8402"/>) aims to enable lightweight path steering
via loose source routing. Compared to its more heavy-weight
predecessor RSVP-TE, SR does for example not require per-path
signaling to each of these hops.
BIER-TE supports the same design philosophy for multicast. Like in
SR, it relies on source-routing - via the definition of a BitString.
Like SR, it only requires to consider the "hops" on which either
replication has to happen, or across which the traffic should be
steered (even without replication). Any other hops can be skipped
via the use of routed adjacencies.
BIER-TE bit position (BP) can be understood as the BIER-TE equivalent
of "forwarding segments" in SR, but they have a different scope than
SR forwarding segments. Whereas forwarding segments in SR are global
or local, BPs in BIER-TE have a scope that is the group of BFR(s)
that have adjacencies for this BP in their BIFT. This can be called
"adjacency" scoped forwarding segments.
Adjacency scope could be global, but then every BFR would need an
adjacency for this BP, for example a forward_routed() adjacency with
encapsulation to the global SR SID of the destination. Such a BP
would always result in ingress replication though (as in [RFC7988]).
The first BFR encountering this BP would directly replicate to it.
Only by using non-global adjacency scope for BPs can traffic be
steered and replicated on non-ingress BFR.
SR can naturally be combined with BIER-TE and help to optimize it.
For example, instead of defining bit positions for non-replicating
hops, it is equally possible to use segment routing encapsulations
(e.g. SR-MPLS label stacks) for the encapsulation of
"forward_routed" adjacencies.
Note that (non-TE) BIER itself can also be seen to be similar to SR.
BIER BPs act as global destination Node-SIDs and the BIER BitString
is simply a highly optimized mechanism to indicate multiple such SIDs
and let the network take care of effectively replicating the packet
hop-by-hop to each destination Node-SID. What BIER does not allow is
to indicate intermediate hops, or in terms of SR the ability to
indicate a sequence of SID to reach the destination. This is what
BIER-TE and its adjacency scoped BP enables.
Authors' Addresses Authors' Addresses
Toerless Eckert (editor) Toerless Eckert (editor)
Futurewei Technologies Inc. Futurewei Technologies Inc.
2330 Central Expy 2330 Central Expy
Santa Clara, 95050 Santa Clara, 95050
United States of America United States of America
Email: tte+ietf@cs.fau.de Email: tte+ietf@cs.fau.de
Gregory Cauchie
Bouygues Telecom
Email: GCAUCHIE@bouyguestelecom.fr
Michael Menth Michael Menth
University of Tuebingen University of Tuebingen
Email: menth@uni-tuebingen.de Email: menth@uni-tuebingen.de
Gregory Cauchie
Bouygues Telecom
Email: GCAUCHIE@bouyguestelecom.fr
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