< draft-ietf-bier-te-arch.txt   draft-ietf-bier-te-arch.txt >
Network Working Group T. Eckert, Ed. Network Working Group T. Eckert, Ed.
Internet-Draft Futurewei Internet-Draft Futurewei
Intended status: Standards Track G. Cauchie Intended status: Standards Track G. Cauchie
Expires: July 28, 2022 Bouygues Telecom Expires: July 31, 2022 Bouygues Telecom
M. Menth M. Menth
University of Tuebingen University of Tuebingen
January 24, 2022 January 27, 2022
Tree Engineering for Bit Index Explicit Replication (BIER-TE) Tree Engineering for Bit Index Explicit Replication (BIER-TE)
draft-ietf-bier-te-arch-12 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 steered replication and forwarding for "Bit Index Explicit
Replication" (BIER, RFC8279) packets. It is called BIER Tree Replication" (BIER, RFC8279) packets. It is called BIER Tree
Engineering (BIER-TE) and is intended to be used as the path steering Engineering (BIER-TE) and is intended to be used as the path steering
mechanism for Traffic 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 BIER in which BPs indicate "Bit-Forwarding Egress Routers" (BFER). A
leverage BIER forwarding engines with little changes. Co-existence BIER-TE packets BitString therefore indicates the edges of the (loop-
of BIER and BIER-TE forwarding in the same domain is possible, for free) tree that the packet is forwarded across by BIER-TE. BIER-TE
example by using separate BIER "sub-domains" (SDs). Except for the can leverage BIER forwarding engines with little changes. Co-
optional routed adjacencies, BIER-TE does not require a BIER routing existence of BIER and BIER-TE forwarding in the same domain is
underlay, and can therefore operate without depending on an "Interior possible, for example by using separate BIER "sub-domains" (SDs).
Gateway 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
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 28, 2022.
This Internet-Draft will expire on July 31, 2022.
Copyright Notice Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 35 skipping to change at page 2, line 38
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 . . . . . . . . . . . . . . . 13
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 . . . . . . . . . 15
3.2.1.4. Link/Node Failures and Recovery . . . . . . . . . 15 3.2.1.4. Link/Node Failures and Recovery . . . . . . . . . 15
3.3. The BIER-TE Forwarding Plane . . . . . . . . . . . . . . 15 3.3. The BIER-TE Forwarding Plane . . . . . . . . . . . . . . 15
3.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 16 3.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 16
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 Bit Index Forwarding Table (BIFT) . . . . . . . . . . 18
4.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 19 4.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 19
4.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 19 4.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 19
4.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 19 4.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 19
4.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 19 4.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2.4. Local Decap(sulation) . . . . . . . . . . . . . . . . 20 4.2.4. Local Decap(sulation) . . . . . . . . . . . . . . . . 20
4.3. Encapsulation / Co-existence with BIER . . . . . . . . . 20 4.3. Encapsulation / Co-existence with BIER . . . . . . . . . 20
4.4. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . 21 4.4. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . 21
4.5. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 24 4.5. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 25
4.6. BFR Requirements for BIER-TE forwarding . . . . . . . . . 27 4.6. BFR Requirements for BIER-TE forwarding . . . . . . . . . 28
5. BIER-TE Controller Operational Considerations . . . . . . . . 28
5. BIER-TE Controller Operational Considerations . . . . . . . . 27 5.1. Bit Position Assignments . . . . . . . . . . . . . . . . 28
5.1. Bit position Assignments . . . . . . . . . . . . . . . . 27 5.1.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . 29
5.1.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . 28 5.1.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . 28 5.1.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . 29
5.1.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . 28 5.1.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . 30
5.1.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . 29 5.1.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . 31
5.1.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . 30 5.1.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . 31
5.1.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . 30 5.1.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . 32
5.1.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . 31 5.1.8. Forward Routed adjacencies . . . . . . . . . . . . . 35
5.1.8. Forward Routed adjacencies . . . . . . . . . . . . . 34 5.1.8.1. Reducing bit positions . . . . . . . . . . . . . 35
5.1.8.1. Reducing bit positions . . . . . . . . . . . . . 34 5.1.8.2. Supporting nodes without BIER-TE . . . . . . . . 36
5.1.8.2. Supporting nodes without BIER-TE . . . . . . . . 35 5.1.9. Reuse of bit positions (without DNC) . . . . . . . . 36
5.1.9. Reuse of bit positions (without DNC) . . . . . . . . 35 5.1.10. Summary of BP optimizations . . . . . . . . . . . . . 38
5.1.10. Summary of BP optimizations . . . . . . . . . . . . . 36 5.2. Avoiding duplicates and loops . . . . . . . . . . . . . . 39
5.2. Avoiding duplicates and loops . . . . . . . . . . . . . . 38 5.2.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . 38 5.2.2. Duplicates . . . . . . . . . . . . . . . . . . . . . 39
5.2.2. Duplicates . . . . . . . . . . . . . . . . . . . . . 38 5.3. Managing SI, sub-domains and BFR-ids . . . . . . . . . . 40
5.3. Managing SI, sub-domains and BFR-ids . . . . . . . . . . 39 5.3.1. Why SI and sub-domains . . . . . . . . . . . . . . . 40
5.3.1. Why SI and sub-domains . . . . . . . . . . . . . . . 39 5.3.2. Assigning bits for the BIER-TE topology . . . . . . . 41
5.3.2. Assigning bits for the BIER-TE topology . . . . . . . 40 5.3.3. Assigning BFR-id with BIER-TE . . . . . . . . . . . . 42
5.3.3. Assigning BFR-id with BIER-TE . . . . . . . . . . . . 41 5.3.4. Mapping from BFR to BitStrings with BIER-TE . . . . . 43
5.3.4. Mapping from BFR to BitStrings with BIER-TE . . . . . 41 5.3.5. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . 44
5.3.5. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . 43 5.3.6. Example bit allocations . . . . . . . . . . . . . . . 44
5.3.6. Example bit allocations . . . . . . . . . . . . . . . 43 5.3.6.1. With BIER . . . . . . . . . . . . . . . . . . . . 44
5.3.6.1. With BIER . . . . . . . . . . . . . . . . . . . . 43 5.3.6.2. With BIER-TE . . . . . . . . . . . . . . . . . . 45
5.3.6.2. With BIER-TE . . . . . . . . . . . . . . . . . . 44 5.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 46
5.3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 45 6. BIER-TE and Segment Routing . . . . . . . . . . . . . . . . . 47
6. BIER-TE and Segment Routing . . . . . . . . . . . . . . . . . 45 7. Security Considerations . . . . . . . . . . . . . . . . . . . 48
7. Security Considerations . . . . . . . . . . . . . . . . . . . 46 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 49
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 50
10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 48 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 60 11.1. Normative References . . . . . . . . . . . . . . . . . . 62
11.1. Normative References . . . . . . . . . . . . . . . . . . 60 11.2. Informative References . . . . . . . . . . . . . . . . . 62
11.2. Informative References . . . . . . . . . . . . . . . . . 60 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 63
1. Overview 1. Overview
BIER-TE is based on architecture, terminology and packet formats with BIER-TE is based on architecture, terminology and packet formats with
(non-TE) BIER as described in [RFC8279] and [RFC8296]. This document (non-TE) BIER as described in [RFC8279] and [RFC8296]. This document
describes BIER-TE in the expectation that the reader is familiar with describes BIER-TE in the expectation that the reader is familiar with
these two documents. 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 "Bit Index Explicit Replication" indicate adjacencies of the network topology, as opposed to (non-TE)
(BIER) in which BPs indicate "Bit-Forwarding Egress Routers" (BFER). BIER in which BPs indicate "Bit-Forwarding Egress Routers" (BFER). A
With BIER-TE, the "Bit Index Forwarding Table" (BIFT) of each "Bit BIER-TE packets BitString therefore indicates the edges of the (loop-
free) tree that the packet is forwarded across by BIER-TE. With
BIER-TE, the "Bit Index Forwarding Table" (BIFT) of each "Bit
Forwarding Router" (BFR) is only populated with BP that are adjacent Forwarding Router" (BFR) is only populated with BP that are adjacent
to the BFR in the BIER-TE Topology. Other BPs are empty in the BIFT. 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 The BFR replicate and forwards BIER packets to adjacent BPs that are
set in the packet. BPs are normally also cleared upon forwarding to set in the packet. BPs are normally also cleared upon forwarding to
avoid duplicates and loops. This is detailed further below. 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 ([RFC8402]). steering in "Segment Routing" (SR) networks ([RFC8402]).
This document is structured as follows: This document is structured as follows:
o Section 2 introduces BIER-TE with two reference forwarding o 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.
o Section 3 describes the components of the BIER-TE architecture, o 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.
o Section 4 specifies the behavior of the BIER-TE forwarding plane o 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.
o Section 5 describes operational considerations for the BIER-TE o 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 "Set Identifier" (SI), "sub-domain" for free), and finally how "Set Identifier" (SI), "sub-domain"
(SD) and BFR-ids can be managed by a BIER-TE controller, examples (SD) and BFR-ids can be managed by a BIER-TE controller, examples
and summary. and summary.
o Section 6 concludes the technology specific sections of document o Section 6 concludes the technology specific sections of the
by further relating BIER-TE to 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
skipping to change at page 6, line 44 skipping to change at page 6, line 44
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 used. All BFRs picture with 6 BFRs. p1...p15 are the bit positions used. All BFRs
can act as an ingress BFR (BFIR), BFR1, BFR3, BFR4 and BFR6 can also can act as an ingress BFR (BFIR), BFR1, BFR3, BFR4 and BFR6 can also
be BFERs. Forward_connected() is the name for adjacencies that are be BFERs. Forward_connected() is the name for adjacencies that are
representing subnet adjacencies of the network. Local_decap() is the representing subnet adjacencies of the network. Local_decap() is the
name of the adjacency to decapsulate BIER-TE packets and pass their name of the adjacency to decapsulate BIER-TE 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,p15). When this packet BitString needs to be (p2,p5,p8,p10,p12,p13,p15). When this packet
is 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.
skipping to change at page 9, line 39 skipping to change at page 9, line 39
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 packet
replication and delivery via a BitString. replication 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 supportable encapsulations including [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, except for how bits have to be 5. The BIER forwarding plane, except for how bits 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
3. The reference option for the core part of the BIER-TE control
plane is the BIER-TE controller. Nevertheless, both BIER and plane is the BIER-TE controller. Nevertheless, both BIER and
BIER-TE BIFT forwarding plane state could equally be BIER-TE BIFT 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. BIRTs are not required on BFRs for BIER-TE when using a BIER-
TE controller because the controller can directly populate TE controller because the controller can directly populate
the BIFTs. In BIER, BIRTs are populated by the distributed the BIFTs. In BIER, BIRTs are populated by the distributed
routing protocol support for BIER, allowing BFRs to populate routing protocol support for BIER, allowing BFRs to populate
skipping to change at page 10, line 44 skipping to change at page 10, line 44
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
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 BIFT. 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 with the intent to easily build/ BIER-TE forwarding rules, especially the Bitstring parsing are
program common forwarding hardware with BIER. The pseudocode in designed to be as close as possible to those of BIER in the
Section 4.4 shows how existing (non-TE) BIER/BIFT forwarding can be expectation that this eases the programming of BIER-TE forwarding
modified to support the REQUIRED BIER-TE forwarding functionality, by code and/or BIER-TE forwarding hardware on platforms supporting BIER.
using BIER BIFT's "Forwarding Bit Mask" (F-BM): Only the clearing of The pseudocode in Section 4.4 shows how existing (non-TE) BIER/BIFT
bits to avoid duplicate packets to a BFR's neighbor is skipped in forwarding can be modified to support the REQUIRED BIER-TE forwarding
BIER-TE forwarding because it is not necessary and could not be done functionality, by using BIER BIFT's "Forwarding Bit Mask" (F-BM):
when using BIER 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->|
|<--------------------->| |<--------------------->|
skipping to change at page 12, line 43 skipping to change at page 12, line 43
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.
2. Determine the per-BFR BIFT from the BIER-TE topology. 2. Determine the per-BFR BIFT from the BIER-TE topology.
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.
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.
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.
2. Determine the BitStrings and optionally Entropy. 2. Determine the BitStrings and optionally Entropy.
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.
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.]
o A single centralized BIER-TE controller. This architecture describes the BIER-TE control plane as shown in
Figure 3 to consists of:
o A single, centralized BIER-TE controller.
o Data-models and protocols to communicate between controller and o Data-models and protocols to communicate between controller and
BFRs in step 1, such as YANG/Netconf/RestConf. BFRs in support of BIER-TE topology control (Paragraph 1), such as
YANG/NETCONF/RESTCONF ([RFC7950]/[RFC6241]/[RFC8040]).
o Protocols to communicate between controller and BFIR in step 2, o Protocols to communicate between controller and BFIR in support of
such as BIER-TE extensions for [RFC5440]. BIER-TE tree control (Paragraph 2), such as BIER-TE extensions for
[RFC5440].
The (non-TE) BIER control plane could equally be implemented without The single, centralized BIER-TE controller is used in this document
any active dynamic components by an operator via CLI on the BFRs. In as reference option for the BIER-TE control plane but other options
that case, operator configured local policy on the BFIR would have to are equally feasible. The BIER-TE control plane could equally be
determine how to set the appropriate BIER header fields. The BIER-TE implemented without automated configuration/protocols, by an operator
control plane could also be decentralized and/or distributed, but via CLI on the BFRs. In that case, operator configured local policy
this document does not consider any additional protocols and/or on the BFIR would have to determine how to set the appropriate BIER
procedures which would then be necessary to coordinate its entities header fields. The BIER-TE control plane could also be decentralized
to achieve the above described functionality. 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 (Paragraph 1) includes
creation. The latter describes the process by which a Controller network topology discovery and BIER-TE topology creation. The latter
determines which routers are to be configured as BFR and the describes the process by which a Controller determines which routers
adjacencies between them. are to be configured as BFR and the 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 BP required and how to assign BP 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 (beside
topology discovery) is ideally via standardized protocols and data- topology discovery) is ideally via standardized protocols and data-
models such as Netconf/RestConf/YANG/PCEP. Vendor-specific CLI on models such as NETCONF/RESTCONF/YANG/PCEP. Vendor-specific CLI on
the BFRs is also an option (as in many other SDN solutions lacking the BFRs is also an option (as in many other SDN solutions lacking
definition of standardized data model). definition of standardized data model).
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
skipping to change at page 16, line 8 skipping to change at page 16, line 21
according to state created by the BIER-TE control plane and/or according to state created by the BIER-TE control plane and/or
overlay layer. 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 BIFT that was populated by the BIER-TE Controller. For every BP the BIFT that was populated by the BIER-TE Controller. For every BP
that is set in the BitString, and that has one or more adjacencies in that is set in the BitString, and that has one or more adjacencies in
the BIFT, a copy is made according to the type of adjacencies for the BIFT, a copy is made according to the type of adjacencies for
that BP in the BIFT. Before sending any copy, the BFR clears all BPs that BP in the BIFT. Before sending any copy, the BFR clears all BPs
in the BitString of the packet for which the BFR has one or more in the BitString of the packet for which the BFR has one or more
adjacencies in the BIFT, except when the adjacency indicates adjacencies in the BIFT. Clearing these bits inhibits packets from
"DoNotClear" (DNC, see Section 4.2.1). This is done to inhibit that looping when the BitStrings erroneously includes a forwarding loop.
packets can loop. Because DNC raises the risk of packets looping When a forward_connected() adjacency has the "DoNotClear" (DNC) flag
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 20 skipping to change at page 17, line 32
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
skipping to change at page 18, line 5 skipping to change at page 18, line 17
4.1. The Bit Index Forwarding Table (BIFT) 4.1. The Bit Index Forwarding Table (BIFT)
The BIFT exists in every BFR. For every sub-domain in use, it is a The BIFT exists in every BFR. For every sub-domain in use, it is a
table indexed by SI:bit position and is populated by the BIER-TE table indexed by SI:bit position and is populated by the BIER-TE
control plane. Each index can be empty or contain a list of one or control plane. Each index can be empty or contain a list of one or
more adjacencies. more adjacencies.
Like BIER, BIER-TE can support multiple sub-domains, each with a Like BIER, BIER-TE can support multiple sub-domains, each with a
separate BIFT. separate BIFT.
In [RFC8279], Figure 2, indices into the BIFT are both SI:BitString In [RFC8279], Figure 2, indices into the BIFT are SI:BitString and
and BFR-id, where BitString is indicating a BP: BFR-id = SI * 2^BSL + BFR-id. BitString is indicating a BP, and therefore: BFR-id = SI:BP
BP. As shown in Figure 4, in BIER-TE, only SI:BP are used as indices = SI * 2^BSL + (BP - 1). As shown in Figure 4, in BIER-TE, only
into a BIFT because they identify adjacencies and not BFR. SI:BP are used as indices into a BIFT because they identify
adjacencies and not BFR.
------------------------------------------------------------------ ------------------------------------------------------------------
| Index: | Adjacencies: | | Index: | Adjacencies: |
| SI:bit position | <empty> or one or more per entry | | SI:bit position | <empty> or one or more per entry |
================================================================== ==================================================================
| 0:1 | forward_connected(interface,neighbor{,DNC}) | | 0:1 | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:2 | forward_connected(interface,neighbor{,DNC}) | | 0:2 | forward_connected(interface,neighbor{,DNC}) |
| | forward_connected(interface,neighbor{,DNC}) | | | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:3 | local_decap({VRF}) | | 0:3 | local_decap({VRF}) |
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:4 | forward_routed({VRF,}l3-neighbor) | | 0:4 | forward_routed({VRF,}l3-neighbor) |
------------------------------------------------------------------ ------------------------------------------------------------------
skipping to change at page 22, line 52 skipping to change at page 23, line 5
In BIER-TE, a BFR-NBR is an adjacency, forward_connected, In BIER-TE, a BFR-NBR is an adjacency, forward_connected,
forward_routed or local_decap. There is no need for [2] to suppress forward_routed or local_decap. There is no need for [2] to suppress
duplicates in the way BIER does because in general, different BP duplicates in the way BIER does because in general, different BP
would never have the same adjacency. If a BIER-TE controller would never have the same adjacency. If a BIER-TE controller
actually finds some optimization in which this would be desirable, actually finds some optimization in which this would be desirable,
then the controller is also responsible to ensure that only one of then the controller is also responsible to ensure that only one of
those bits is set in any Packet->BitString, unless the controller those bits is set in any Packet->BitString, unless the controller
explicitly wants for duplicates to be created. 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):
o This pseudocode eliminates per-bit F-BM, therefore reducing the o 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 BitStringLength^2*SI and eliminating the
need for per-packet-copy bit string operation except for need for per-packet-copy BitString operation except for
adjacencies with the DNC flag set: adjacencies with the DNC flag set:
* AdjacentBits[SI] are bit positions with a non-empty list of * AdjacentBits[SI] are bit positions with a non-empty list of
adjacencies in this BFR BIFT. This can be computed whenever adjacencies in this BFR BIFT. This can be computed whenever
the BIER-TE Controller updates (add/removes) adjacencies in the the BIER-TE Controller updates (add/removes) adjacencies in the
BIFT. BIFT.
* The BFR needs to create packet copies for these adjacent bits * The BFR needs to create packet copies for these adjacent bits
when they are set in the packets BitString. This set of bits when they are set in the packets BitString. This set of bits
is calculated in PktAdjacentBits. is calculated in PktAdjacentBits.
* All bit positions to which the BFR creates copies have to be * All bit positions to which the BFR creates copies have to be
cleared in packet copies to avoid loops. This is done by cleared in packet copies to avoid loops. This is done by
masking the bit string of the packet with ~AdjacentBits[SI]. masking the BitString of the packet with ~AdjacentBits[SI].
When an adjacency has DNC set, this bit position is set again When an adjacency has DNC set, this bit position is set again
only for the packet copy towards that bit position. only for the packet copy towards that bit position.
o BIFT entries may contain more than one adjacency in support of o BIFT entries may contain more than one adjacency in support of
specific configurations such as Section 5.1.5. The code therefore specific configurations such as Section 5.1.5. The code therefore
includes a loop over these adjacencies. includes a loop over these adjacencies.
o The ECMP adjacency is shown. Its parameters are a seed and a o The ECMP adjacency is shown. Its parameters are a seed and a
ListOfAdjacencies from which one is picked. ListOfAdjacencies from which one is picked.
skipping to change at page 27, line 16 skipping to change at page 28, line 16
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 that support BIER-TE and BIER MUST support configuration that BFR that support BIER-TE and BIER MUST support configuration that
enables BIER-TE instead of (non-TE) BIER forwarding rules for all enables BIER-TE instead of (non-TE) BIER forwarding rules for all
BIFT of one or more BIER sub-domains. Every BP in a BIER-TE BIFT BIFT of one or more BIER sub-domains. Every BP in a BIER-TE BIFT
MUST support to have zero or one adjacency. BIER-TE forwarding MUST MUST support to have zero or one adjacency. BIER-TE forwarding MUST
support the adjacency types forward_connected() with clear DNC flag, support the adjacency types forward_connected() with the DNC flag not
forward_routed() and local_decap. As explained in Section 4.4, these set, forward_routed() and local_decap. As explained in Section 4.4,
REQUIRED BIER-TE forwarding functions can be implementeded via the these REQUIRED BIER-TE forwarding functions can be implementeded via
same Forwarding Pseudocode as BIER forwarding except for one the same Forwarding Pseudocode as BIER forwarding except for one
modification (skipping one masking with F-BM). 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&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 ECMP
scenarios, see Section 5.1.7 for an example. This is a MAY scenarios, see Section 5.1.7 for an example. This is a MAY
requirement, because the deployment importance of ECMP adjacencies requirement, because the deployment importance of ECMP adjacencies
for BIER-TE is unclear as one can also leverage ECMP of the routing for BIER-TE is unclear as one can also leverage ECMP of the routing
underlay via forwarded_routed adjacencies and/or might prefer to have underlay via forwarded_routed adjacencies and/or might prefer to have
more explicit control of the path chosen via explicit BP/adjacencies more explicit control of the path chosen via explicit BP/adjacencies
for each ECMP path alternative. for each ECMP path 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 BFR, the same bit position can be
used on both BFR for the adjacency to the neighboring BFR. A P2P used on both BFR 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 local_decap
skipping to change at page 28, line 31 skipping to change at page 29, line 31
| / \ | | | | / \ | | |
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
skipping to change at page 29, line 41 skipping to change at page 30, line 41
packet, then these two optimizations can not be used together with packet, then these two optimizations can not be used together with
shared bit positions optimization for leaf-BFER. 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 31, line 36 skipping to change at page 32, line 36
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)
[RFC-Editor: A reviewer (Lars Eggert) noted that the infinite "to [RFC-Editor: A reviewer (Lars Eggert) noted that the infinite "to
use" in the following sentence is not correct. The same was also use" in the following sentence is not correct. The same was also
noted for several other similar instances. What exactly should be noted for several other similar instances. The following URL seems
done about this ?]. 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 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 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 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 connects BFR1 and BFR2, and only one BP is used instead of three BP
to deliver packets from BFR1 to BFR2. to deliver packets from BFR1 to BFR2.
--L1----- --L1-----
BFR1 --L2----- BFR2 BFR1 --L2----- BFR2
--L3----- --L3-----
skipping to change at page 34, line 47 skipping to change at page 36, line 8
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 path in the routing flows that have arrived at BFR1 or BFR4 via a path in the 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 BFR 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.
skipping to change at page 41, line 13 skipping to change at page 42, line 24
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 BFR 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, BFIR 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 * 2^BSL + (BP - 1), such that the SI and BP of a
can be calculated from the BFR-id and vice versa. This also means BFER can be calculated from the BFR-id and vice versa. This also
that every BFR with a BFR-id has a reserved BP in an SI, even if that means that every BFR with a BFR-id has a reserved BP in an SI, even
is not necessary for BIER forwarding, because the BFR may never be a if that is not necessary for BIER forwarding, because the BFR may
BFER but only a BFIR. never be a 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 be determined using the same procedure as such a BFER can therefore be determined using the same procedure as
in (non-TE) BIER: BFR-id = SI * BitStringLength + BP. in (non-TE) BIER: BFR-id = SI * BitStringLength + (BP - 1).
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 local_decap() adjacency. Likewise, BFIR who are not also BFER may
not have a unique local_decap() adjacency either. For all those BFIR not have a unique local_decap() adjacency either. For all those BFIR
and (leaf) BFER, the controller needs to determine unique BFR-ids and (leaf) BFER, the controller needs to determine unique BFR-ids
that do not collide with the BFR-ids derived from the non-leaf BFER that do not collide with the BFR-ids derived from the non-leaf BFER
local_decap() BPs. local_decap() BPs.
While this document defines no requirements how to allocate such BFR- While this document defines no requirements how to allocate such BFR-
id, a simple option is to derive it from the (SI,BP) of an adjacency id, a simple option is to derive it from the (SI,BP) of an adjacency
skipping to change at page 42, line 8 skipping to change at page 43, line 19
could be the first BP with an adjacency towards that BFER. 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 BFER
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
skipping to change at page 42, line 44 skipping to change at page 44, line 7
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 BIER-TE controller
requires some way to identify BFER. If BFR-ids are used in the requires some way to identify BFER. If BFR-ids are used in the
deployment, as outlined in Section 5.3.3, then those are the natural deployment, as outlined in Section 5.3.3, then those are the natural
BFR identifier. If BFR-ids are not used, then any other unique BFR identifier. If BFR-ids are not used, then any other unique
identifier, such as the BFR-prefix of the BFR as of [RFC8279] could identifier, such as the BFR-prefix of the BFR as of [RFC8279] could
be used. 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 44, line 10 skipping to change at page 45, line 28
(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
skipping to change at page 45, line 26 skipping to change at page 46, line 44
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:BP = SI * 2^BSL + (BP -
specific functions in any possible BIER layer control plane used in 1). This allows to re-use the BIER architecture concept of BFR-id
conjunction with BIER-TE, flow overlay methods and BIER headers. and therefore 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.
skipping to change at page 47, line 30 skipping to change at page 48, line 51
BFR in a domain causes no impairment of the BIER-TE control plane on BFR in a domain causes no impairment of the BIER-TE control plane on
other BFR. If a routing protocol is used to support forward_routed() other BFR. If a routing protocol is used to support forward_routed()
adjacencies, then this is still an attack vector as in BIER, but only adjacencies, then this is still an attack vector as in BIER, but only
for BIER-TE forward_routed() adjacencies, and not other adjacencies. 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 48, line 36 skipping to change at page 50, line 10
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,
Carsten Borman and Wolfgang Braun for their reviews and suggestions. Carsten Borman and Wolfgang Braun for their reviews and suggestions.
Special thanks to Xuesong Geng for shepherding the document and for Special thanks to Xuesong Geng for shepherding the document and for
IESG review/suggestions by Alvaro Retana (responsible AD/RTG), IESG review/suggestions by Alvaro Retana (responsible AD/RTG),
Benjamin Kaduk (SEC), Tommy Pauly (TSV), Zaheduzzaman Sarker (TSV), Benjamin Kaduk (SEC), Tommy Pauly (TSV), Zaheduzzaman Sarker (TSV),
Eric Vyncke (INT), Martin Vigoureux (RTG), Robert Wilton (OPS), Eric Eric Vyncke (INT), Martin Vigoureux (RTG), Robert Wilton (OPS), Eric
Kline (INT), Lars Eggert (GEN), Roman Danyliv (SEC), Ines Robles Kline (INT), Lars Eggert (GEN), Roman Danyliv (SEC), Ines Robles
(RTGDIR). (RTGDIR), Robert Sparks (Gen-ART), Yingzhen Qu (RTGdir), Martin Duke
(TSV).
10. Change log [RFC Editor: Please remove] 10. Change log [RFC Editor: Please remove]
draft-ietf-bier-te-arch: draft-ietf-bier-te-arch:
12: 12:
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 broken SI*BSL formulas to SI * 2^BSL.
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. RTGDIR review Ines Robles.
Fixed up adjacencies in Example 2 and explanation text to be Fixed up adjacencies in Example 2 and explanation text to be
explicit about which BFR not only passes, but also receives the explicit about which BFR not only passes, but also receives the
packet. packet.
7. (security considerations). Added paragraph about 7. (security considerations). Added paragraph about
forward_routed() and prohibiting BIER packet leaking in/out of forward_routed() and prohibiting BIER packet leaking in/out of
domain. domain.
skipping to change at page 62, line 10 skipping to change at page 64, line 24
[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>.
 End of changes. 81 change blocks. 
216 lines changed or deleted 310 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/