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In: Expert_Review
MPLS WG K. Kompella
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track L. Contreras
Expires: April 25, 2020 Telefonica
October 23, 2019
Resilient MPLS Rings
draft-ietf-mpls-rmr-12
Abstract
This document describes the use of the MPLS control and data planes
on ring topologies. It describes the special nature of rings, and
proceeds to show how MPLS can be effectively used in such topologies.
It describes how MPLS rings are configured, auto-discovered and
signaled, as well as how the data plane works. Companion documents
describe the details of discovery and signaling for specific
protocols.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 5
3.1. Provisioning . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Ring Nodes . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Ring Links and Directions . . . . . . . . . . . . . . . . 6
3.3.1. Express Links . . . . . . . . . . . . . . . . . . . . 6
3.4. Ring LSPs . . . . . . . . . . . . . . . . . . . . . . . . 7
3.5. Installing Primary LFIB Entries . . . . . . . . . . . . . 7
3.6. Protection . . . . . . . . . . . . . . . . . . . . . . . 7
3.7. Installing FRR LFIB Entries . . . . . . . . . . . . . . . 8
4. Autodiscovery . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Ring Announcement Phase . . . . . . . . . . . . . . . . . 10
4.3. Mastership Phase . . . . . . . . . . . . . . . . . . . . 11
4.4. Ring Identification Phase . . . . . . . . . . . . . . . . 11
4.5. Ring Changes . . . . . . . . . . . . . . . . . . . . . . 12
5. Ring OAM . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Advanced Topics . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Half-rings . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Hub Node Resilience . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Rings are a very common topology in transport networks. A ring is
the simplest topology offering link and node resilience. Rings are
nearly ubiquitous in access and aggregation networks. As MPLS
increases its presence in such networks, and takes on a greater role
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in transport, it is imperative that MPLS handles rings well; this is
not the case today.
This document describes the special nature of rings, and the special
needs of MPLS on rings. It then shows how these needs can be met in
several ways, some of which involve extensions to protocols such as
IS-IS [RFC5305], OSPF[RFC3630], RSVP-TE [RFC3209] and LDP [RFC5036].
RMR LSPs can also be signaled with SPRING [RFC8402]; that will be
described in a future document.
The intent of this document is to handle rings that "occur
naturally". Many access and aggregation networks in metros have
their start as a simple ring. They may then grow into more complex
topologies, for example, by adding parallel links to the ring, or by
adding "express" links. The goal here is to discover these rings
(with some guidance), and run MPLS over them efficiently. The intent
is not to construct rings in a mesh network, and use those for
protection.
1.1. Definitions
A (directed) graph G = (V, E) consists of a set of vertices (or
nodes) V and a set of edges (or links) E. An edge is an ordered pair
of nodes (a, b), where a and b are in V. (In this document, the
terms node and link will be used instead of vertex and edge.)
A ring is a subgraph of G. A ring consists of a subset of n nodes
{R_i, 0 <= i < n} of V. The directed edges {(R_i, R_i+1) and (R_i+1,
R_i), 0 <= i < n-1} must be a subset of E (note that index arithmetic
is done modulo n). We define the direction from node R_i to R_i+1 as
"clockwise" (CW) and the reverse direction as "anticlockwise" (AC).
As there may be several rings in a graph, we number each ring with a
distinct ring ID RID.
R0 . . . R1
. .
R7 R2
Anti- | . Ring . |
Clockwise | . . | Clockwise
v . RID = 17 . v
R6 R3
. .
R5 . . . R4
Figure 1: Ring with 8 nodes
The following terminology is used for ring LSPs:
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Ring ID (RID): A non-negative number. When the RID identifies a
ring, it must be positive and unique in some scope of a Service
Provider's network. An RID of zero, when assigned to a node,
indicates that the node must behave in "promiscuous mode" (see
Section 3.2). A node may belong to multiple rings.
Ring node: A member of a ring. Note that a device may belong to
several rings.
Node index: A logical numbering of nodes in a ring, from zero up to
one less than the ring size. Used purely for exposition in this
document.
Ring master: The ring master initiates the ring identification
process. Mastership is indicated in the IGP by a two-bit field.
Ring neighbors: Nodes whose indices differ by one (modulo ring
size).
Ring links: Links that connect ring neighbors.
Express links: Links that connect non-neighboring ring nodes.
Ring direction: A two-bit field in the IGP indicating the direction
of a link. The choices are:
UN: 00 undefined link
CW: 01 clockwise ring link
AC: 10 anticlockwise ring link
EX: 11 express link
Ring Identification: The process of discovering ring nodes, ring
links, link directions, and express links.
The following notation is used for ring LSPs:
R_k: A ring node with index k. R_k has AC neighbor R_(k-1) and CW
neighbor R_(k+1).
RL_k: A (unicast) Ring LSP anchored on node R_k.
CL_jk: A label allocated by R_j for RL_k in the CW direction.
AL_jk: A label allocated by R_j for RL_k in the AC direction.
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2. Motivation
A ring is the simplest topology that offers resilience. This is
perhaps the main reason to lay out fiber in a ring. Thus, effective
mechanisms for fast failover on rings are needed. Furthermore, there
are large numbers of rings. Thus, configuration of rings needs to be
as simple as possible. Finally, bandwidth management on access rings
is very important, as bandwidth is generally quite constrained here.
The goals of this document are to present mechanisms for improved
MPLS-based resilience in ring networks (using ideas that are
reminiscent of Bidirectional Line Switched Rings), for automatic
bring-up of LSPs, better bandwidth management and for auto-hierarchy.
These goals can be achieved using extensions to existing IGP and MPLS
signaling protocols, using central provisioning, or in other ways.
3. Theory of Operation
Say a ring has ring ID RID. The ring is provisioned by choosing one
or more ring masters for the ring and assigning them the RID. Other
nodes in the ring may also be assigned this RID, or may be configured
as "promiscuous". Ring discovery then kicks in. When each ring node
knows its CW and AC ring neighbors and its ring links, and all
express links have been identified, ring identification is complete.
Once ring identification is complete, each node signals one or more
ring LSPs RL_i. RL_i, anchored on node R_i, consists of two counter-
rotating unicast LSPs that start and end at R_i. A ring LSP is
"multipoint": any node R_j can use RL_i to send traffic to R_i; this
can be in either the CW or AC directions, or both (i.e., load
balanced). Both of these counter-rotating LSPs are "active"; the
choice of direction to send traffic to R_i is determined by policy at
the node where traffic is injected into the ring. The default policy
is to send traffic along the shortest path. Bidirectional
connectivity between nodes R_i and R_j is achieved by using two
different ring LSPs: R_i uses RL_j to reach R_j, and R_j uses RL_i to
reach R_i.
3.1. Provisioning
The goal here is to provision rings with the absolute minimum
configuration. The exposition below aims to achieve that using auto-
discovery via a link-state IGP (see Section 4). Of course, auto-
discovery can be overriden by configuration. For example, a link
that would otherwise be classified by auto-discovery as a ring link
might be configured not to be used for ring LSPs.
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3.2. Ring Nodes
Ring nodes have a loopback address, and run a link-state IGP and an
MPLS signaling protocol. To provision a node as a ring node for ring
RID, the node is simply assigned that RID. A node may be part of
several rings, and thus may be assigned several ring IDs.
To simplify ring provisioning even further, a node N may be made
"promiscuous" by being assigned an RID of 0. A promiscuous node
listens to RIDs in its IGP neighbors' link-state updates. For every
non-zero RID N hears from a neighbor, N joins the corresponding ring
by taking on that RID. In many situations, the use of promiscuous
mode means that only one or two nodes in a ring needs to be
provisioned; everything else is auto-discovered.
A ring node indicates in its IGP updates the ring LSP signaling
protocols it supports. This can be LDP and/or RSVP-TE. Ideally,
each node should support both.
3.3. Ring Links and Directions
Ring links must be MPLS-capable. They are by default unnumbered,
point-to-point (from the IGP point of view) and "auto-bundled". The
"auto-bundled" attribute means that parallel links between ring
neighbors are considered as a single link, without the need for
explicit configuration for bundling (such as a Link Aggregation
Group). Note that each component may be advertised separately in the
IGP; however, signaling messages and labels across one component link
apply to all components. Parallel links between a pair of ring nodes
is often the result of having multiple lambdas or fibers between
those nodes. RMR is primarily intended for operation at the packet
layer; however, parallel links at the lambda or fiber layer may
result in parallel links at the packet layer.
A ring link is not provisioned as belonging to the ring; it is
discovered to belong to ring RID if both its adjacent nodes belong to
RID. A ring link's direction (CW or AC) is also discovered; this
process is initiated by the ring's ring master. Note that the above
two attributes can be overridden by provisioning if needed; it is
then up to the provisioning system to maintain consistency across the
ring.
3.3.1. Express Links
Express links are discovered once ring nodes, ring links and
directions have been established. As defined earlier, express links
are links joining non-neighboring ring nodes; often, this may be the
result of optically bypassing ring nodes.
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3.4. Ring LSPs
Ring LSPs are not provisioned. Once a ring node R_i knows its RID,
its ring links and directions, it kicks off ring LSP signaling
automatically. R_i allocates CW and AC labels for each ring LSP
RL_k. R_i also initiates the creation of RL_i. As the signaling
propagates around the ring, CW and AC labels are exchanged. When R_i
receives CW and AC labels for RL_k from its ring neighbors, primary
and fast reroute (FRR) paths for RL_k are installed at R_i.
For RSVP-TE LSPs, bandwidths may be signaled in both directions.
However, these are not provisioned either; rather, one does "reverse
call admission control". When a service needs to use an LSP, the
ring node where the traffic enters the ring attempts to increase the
bandwidth on the LSP to the egress. If successful, the service is
admitted to the ring.
3.5. Installing Primary LFIB Entries
In setting up RL_k, a node R_j sends out two labels: CL_jk to R_j-1
and AL_jk to R_j+1. R_j also receives two labels: CL_j+1,k from
R_j+1, and AL_j-1,k from R_j-1. R_j can now set up the forwarding
entries for RL_k. In the CW direction, R_j swaps incoming label
CL_jk with CL_j+1,k with next hop R_j+1; these allow R_j to act as
LSR for RL_k. R_j also installs an LFIB entry to push CL_j+1,k with
next hop R_j+1 to act as ingress for RL_k. Similarly, in the AC
direction, R_j swaps incoming label AL_jk with AL_j-1,k with next hop
R_j-1 (as LSR), and an entry to push AL_j-1,k with next hop R_j-1 (as
ingress).
Clearly, R_k does not act as ingress for its own LSPs. However, R_k
can send OAM messages, for example, an MPLS ping or traceroute
([I-D.ietf-mpls-rfc4379bis]), using labels CL_k,k+1 and AL_k-1,k, to
test the entire ring LSP anchored at R_k in both directions.
Furthermore, if these LSPs use Ultimate Hop Popping, then R_k
installs LFIB entries to pop CL_k,k for packets received from R_k-1
and to pop AL_k,k for packets received from R_k+1.
3.6. Protection
In this scheme, there are no protection LSPs as such -- no node or
link bypass LSPs, no standby LSPs, no detours, and no LFA-type
protection. Protection is via the "other" direction around the ring,
which is why ring LSPs are in counter-rotating pairs. Protection
works in the same way for link, node and ring LSP failures.
If a node R_j detects a failure from R_j+1 -- either all links to
R_j+1 fail, or R_j+1 itself fails, R_j switches traffic on all CW
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ring LSPs to the AC direction using the FRR LFIB entries. If the
failure is specific to a single ring LSP, R_j switches traffic just
for that LSP. In either case, this switchover can be very fast, as
the FRR LFIB entries can be preprogrammed. Fast detection and fast
switchover lead to minimal traffic loss.
R_j then sends an indication to R_j-1 that the CW direction is not
working, so that R_j-1 can similarly switch traffic to the AC
direction. For RSVP-TE, this indication can be a PathErr or a
Notify; other signaling protocols have similar indications. These
indications propagate AC until each traffic source on the ring AC of
the failure uses the AC direction. Thus, within a short period,
traffic will be flowing in the optimal path, given that there is a
failure on the ring. This contrasts with (say) bypass protection,
where until the ingress recomputes a new path, traffic will be
suboptimal.
Note that the failure of a node or a link will not necessarily affect
all ring LSPs. Thus, it is important to identify the affected LSPs
(and switch them), but to leave the rest alone.
One point to note is that when a ring node, say R_j, fails, RL_j is
clearly unusable. However, the above protection scheme will cause a
traffic loop: R_j-1 detects a failure CW, and protects by sending CW
traffic on RL_j back all the way to R_j+1, which in turn sends
traffic to R_j-1, etc. There are three proposals to avoid this:
1. Each ring node acting as ingress sends traffic with a TTL of at
most 2*n, where n is the number of nodes in the ring.
2. A ring node sends protected traffic (i.e., traffic switched from
CW to AC or vice versa) with TTL just large enough to reach the
egress.
3. A ring node sends protected traffic with a special purpose label
below the ring LSP label. A protecting node first checks for the
presence of this label; if present, it means that the traffic is
looping and MUST be dropped.
It is recommended that (2) be implemented. The other methods are
optional.
3.7. Installing FRR LFIB Entries
At the same time that R_j sets up its primary CW and AC LFIB entries,
it can also set up the protection forwarding entries for RL_k. In
the CW direction, R_j sets up an FRR LFIB entry to swap incoming
label CL_jk with AL_j-1,k with next hop R_j-1. In the AC direction,
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R_j sets up an FRR LFIB entry to swap incoming label AL_jk with
CL_j+1,k with next hop R_j+1. Again, R_k does not install FRR LFIB
entries in this manner.
Say R1 receives label L42 from R2 to reach R4 in the clockwise
direction, and receives label L40 from R0 to reach R4 in the anti-
clockwise direction. Say R1 also receives label L52 from R2 to reach
R5 in the clockwise direction, and receives label L50 from R0 to
reach R5 in the anti-clockwise direction. R1 makes the following
LFIB entries:
+------+--------+-----------+--------+-----------+
| Dest | CW/NH | CW FRR/NH | AC/NH | AC FRR/NH |
+------+--------+-----------+--------+-----------+
| ... | | | | |
| R4 | L42/R2 | L40/R0 | L40/R0 | L42/R2 |
| R5 | L52/R2 | L50/R0 | L50/R0 | L52/R2 |
| ... | | | | |
+------+--------+-----------+--------+-----------+
R1's LFIB
4. Autodiscovery
4.1. Overview
Auto-discovery proceeds in three phases. The first phase is the
announcement phase. The second phase is the mastership phase. The
third phase is the ring identification phase.
S1
/ \
| R0 . . . R1 R0 has MV = 11
| . \ . R1 has MV = 10
R7 \________ R2 All other nodes have MV = 00
Anti- | . . |
clockwise | . Ring . | Clockwise
v . RID = 17 . v
R6 R3
. .
R5 . . . R4
\ /
\ /
An
Figure 2: Ring with non-ring nodes and links
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The format of an RMR Node Type-Length-Value (TLV) is given below. It
consists of information pertaining to the node and optionally, sub-
TLVs. A Neighbor sub-TLV contains information pertaining to the
node's neighbors. Other sub-TLVs may be defined in the future.
Details of the format specific to IS-IS and OSPF will be given in the
corresponding IGP documents.
[RMR Node Type][RMR Node Length][RID][Node Flags][sub-TLVs]
Ring Node TLV Format
[RMR Nbr Type][RMR Nbr Length][Nbr Address][Nbr Flags]
Ring Neighbor Sub-TLV Format
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MV | SS | SO | MBZ |SU |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MV: Mastership Value
SS: Supported Signaling Protocols
(100 = RSVP-TE; 010 = LDP; 001 = SPRING)
MBZ: Must be zero
SO: Supported OAM Protocols (100 = BFD; 010 = CFM; 001 = EFM)
SU: Signaling Protocol to Use (00 = none; 01 = LDP; 10 = RSVP-TE)
M : Elected Master (0 = no, 1 = yes)
Flags for a Ring Node TLV
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RD |OAM| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RD: Ring Direction
OAM: OAM Protocol to use (00 = none; 01 = BFD; 10 = CFM; 11 = EFM)
MBZ: Must be zero
Flags for a Ring Neighbor TLV
4.2. Ring Announcement Phase
Each node participating in an MPLS ring is assigned an RID; in the
example, RID = 17. A node is also provisioned with a mastership
value. Each node advertises a ring node TLV for each ring it is
participating in, along with the associated flags. It then starts
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timer T1; this timer is to allow each node time to hear from all
other nodes in the ring.
A node in promiscuous mode doesn't advertise any ring node TLVs.
However, when it hears a ring node TLV from an IGP neighbor, it joins
that ring, and sends its own ring node TLV with that RID.
The announcement phase allows a ring node to discover other ring
nodes in the same ring so that a ring master can be elected.
4.3. Mastership Phase
When timer T1 fires, a node enters the mastership phase. In this
phase, each ring node N starts timer T2 and checks if it is master.
If it is the node with the lowest loopback address of all nodes with
the highest mastership values, N declares itself master by
readvertising its ring node TLV with the M bit set.
When timer T2 fires, each node examines the ring node TLVs from all
other nodes in the ring to identify the ring master. There should be
exactly one; if not, each node restarts timer T2 and tries again.
Barring software bugs or malicious code, the principal reason for
multiple nodes for setting their M bit is late-arriving ring
announcements. Say nodes N1 and N2 have the highest mastership
values, and N1 has the lowest loopback address, while N2 has the
second lowest loopback address. If N1 makes its ring announcement
just as N2's T1 timer fires, both N1 and N2 will think they are the
master (since N2 will not have heard N1's announcment in time).
However, in the next round, N2 will realize that N1 is indeed the
master. In the worst case, the mastership phase will occur as many
times as there are nodes in the ring.
4.4. Ring Identification Phase
R0 . . . R1 <------ 3. Anti-clockwise neighbor
. .
R7 R2 <--- 0. Ring Master
. Ring / .
. / . 1. Maximal ring includes R3
. / .
R6 / R3 <--- 2. Clockwise neighbor
. / .
R5 . . . R4 <------ 4. R4 is express neighbor
Figure 3: Ring Identification
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When there is exactly one ring master M (here, R2), M enters the Ring
Identification Phase. M indicates that it has successfully completed
this phase by advertising ring link TLVs. This is the trigger for
M's CW neighbor to enter the Ring Identification Phase. This phase
passes CW until all ring nodes have completed ring identification.
In the Ring Identification Phase, a node X that has two or more IGP
neighbors that belong to the ring picks one of them to be its CW ring
neighbor. If X is the ring master, it also picks a node as its AC
ring neighbor. If there are exactly two such nodes, this step is
trivial. If not, X computes a ring that includes all nodes that have
completed the Ring Identification Phase (as seen by their ring link
TLVs) and further contains the maximal number of nodes that belong to
the ring. Based on that, X picks a CW neighbor and inserts ring link
TLVs with ring direction CW for each link to its CW neighbor; X also
inserts a ring link TLV with direction AC for each link to its AC
neighbor. Then, X determines its express links. These are links
connected to ring nodes that are not ring neighbors. X advertises
ring link TLVs for express links by setting the link direction to
"express link".
Here, R2 has R1 as its neighbor on one side; it has two choices, R3
and R4 on the other. It picks R3 to get a maximal ring (Step 1). It
then picks R3 as its CW neighbor (Step 2) and R1 as its AC neighbor
(Step 3). Finally, it declares the link to R4 as an express link.
4.5. Ring Changes
The main changes to a ring are:
ring link addition;
ring link deletion;
ring node addition; and
ring node deletion.
The main goal of handling ring changes is (as much as possible) not
to perturb existing ring operation. Thus, if the ring master hasn't
changed, all of the above changes should be local to the point of
change. Link adds just update the IGP; signaling should take
advantage of the new capacity as soon as it learns. Link deletions
in the case of parallel links also show up as a change in capacity
(until the last link in the bundle is removed.)
The removal of the last ring link between two nodes, or the removal
of a ring node is an event that triggers protection switching. In a
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simple ring, the result is a broken ring. However, if a ring has
express links, then it may be able to converge to a smaller ring with
protection.
The addition of a new ring node can also be handled incrementally.
5. Ring OAM
Each ring node should advertise in its ring node TLV the OAM
protocols it supports. Each ring node is expected to run a link-
level OAM over each ring link. This should be an OAM protocol that
both neighbors agree on. The default hello time is 3.3 millisecond.
Each ring node also sends OAM messages over each direction of its
ring LSP. This is a multi-hop OAM to check LSP liveness; typically,
BFD would be used for this. The node chooses the hello interval; the
default is once a second.
6. Advanced Topics
6.1. Half-rings
In some cases, a ring H may be incomplete, either because H is
permanently missing a link (not just because of a failure), or
because the link required to complete H is in a different IGP area.
Either way, the ring discovery algorithm will fail. We call such a
ring a "half-ring". Half-rings are sufficiently common that finding
a way to deal with them effectively is a useful problem to solve.
This topic will not be addressed in this document; that task is left
for a future document.
6.2. Hub Node Resilience
Let's call the node(s) that connect a ring to the rest of the network
"hub node(s)" (usually, there are a pair of hub nodes.) Suppose a
ring has two hub nodes H1 and H2. Suppose further that a non-hub
ring node X wants to send traffic to some node Z outside the ring.
This could be done, say, by having targeted LDP (T-LDP) sessions from
H1 and H2 to X advertising LDP reachability to Z via H1 (H2); there
would be a two-label stack from X to reach Z. Say that to reach Z, X
prefers H1; thus, traffic from X to Z will first go to H1 via a ring
LSP, then to Z via LDP.
If H1 fails, traffic from X to Z will drop until the T-LDP session
from H1 to Z fails, the IGP reconverges, and H2's label to Z is
chosen. Thereafter, traffic will go from X to H2 via a ring LSP,
then to Z via LDP. However, this convergence could take a long time.
Since this is a very common and important situation, it is again a
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useful problem to solve. However, this topic too will not be
addressed in this document; that task is left for a future document.
7. Security Considerations
This document proposes extensions to IS-IS, OSPF, LDP and RSVP-TE,
all of which have mechanisms to secure them. The extensions proposed
do not represent per se a compromise to network security when the
control plane is secured, since any manipulation of the content of
the messages or even the control plane misinterpretation of the
semantics are avoided.
8. Acknowledgments
Many thanks to Pierre Bichon whose exemplar of self-organizing
networks and whose urging for ever simpler provisioning led to the
notion of promiscuous nodes.
9. IANA Considerations
There are no requests as yet to IANA for this document.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References
[I-D.ietf-mpls-rfc4379bis]
Kompella, K., Swallow, G., Pignataro, C., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", draft-ietf-mpls-
rfc4379bis-09 (work in progress), October 2016.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
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Internet-Draft Resilient MPLS Rings October 2019
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <https://www.rfc-editor.org/info/rfc5036>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Authors' Addresses
Kireeti Kompella
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale, CA 94089
USA
Email: kireeti.kompella@gmail.com
Luis M. Contreras
Telefonica
Ronda de la Comunicacion
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://people.tid.es/LuisM.Contreras/
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