draft-ietf-rtgwg-remote-lfa-06.txt   draft-ietf-rtgwg-remote-lfa-07.txt 
Network Working Group S. Bryant Network Working Group S. Bryant
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Standards Track S. Previdi Intended status: Standards Track S. Previdi
Expires: November 24, 2014 Cisco Systems Expires: March 29, 2015 Cisco Systems
M. Shand M. Shand
Independent Contributor Independent Contributor
N. So N. So
Tata Communications Vinci Systems
May 23, 2014 September 25, 2014
Remote LFA FRR Remote LFA FRR
draft-ietf-rtgwg-remote-lfa-06 draft-ietf-rtgwg-remote-lfa-07
Abstract Abstract
This draft describes an extension to the basic IP fast re-route This draft describes an extension to the basic IP fast re-route
mechanism described in RFC5286, that provides additional backup mechanism described in RFC5286, that provides additional backup
connectivity for point to point link failures when none can be connectivity for point to point link failures when none can be
provided by the basic mechanisms. provided by the basic mechanisms.
Requirements Language 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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119]. document are to be interpreted as described in RFC2119 [RFC2119].
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
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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 November 24, 2014. This Internet-Draft will expire on March 29, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Repair Paths . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Repair Paths . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Tunnels as Repair Paths . . . . . . . . . . . . . . . . . 6 3.1. Tunnels as Repair Paths . . . . . . . . . . . . . . . . . 6
3.2. Tunnel Requirements . . . . . . . . . . . . . . . . . . . 6 3.2. Tunnel Requirements . . . . . . . . . . . . . . . . . . . 6
4. Construction of Repair Paths . . . . . . . . . . . . . . . . . 7 4. Construction of Repair Paths . . . . . . . . . . . . . . . . 7
4.1. Identifying Required Tunneled Repair Paths . . . . . . . . 7 4.1. Identifying Required Tunneled Repair Paths . . . . . . . 7
4.2. Determining Tunnel End Points . . . . . . . . . . . . . . 7 4.2. Determining Tunnel End Points . . . . . . . . . . . . . . 8
4.2.1. Computing Repair Paths . . . . . . . . . . . . . . . . 8 4.2.1. Computing Repair Paths . . . . . . . . . . . . . . . 8
4.2.2. Selecting Repair Paths . . . . . . . . . . . . . . . . 10 4.2.2. Selecting Repair Paths . . . . . . . . . . . . . . . 10
4.3. A Cost Based RLFA Algorithm . . . . . . . . . . . . . . . 11 4.3. A Cost Based RLFA Algorithm . . . . . . . . . . . . . . . 11
4.4. Interactions with IS-IS Overload, RFC 3137, and Costed 4.4. Interactions with IS-IS Overload, RFC 3137, and Costed
Out Links . . . . . . . . . . . . . . . . . . . . . . . . 16 Out Links . . . . . . . . . . . . . . . . . . . . . . . . 16
5. Example Application of Remote LFAs . . . . . . . . . . . . . . 17 5. Example Application of Remote LFAs . . . . . . . . . . . . . 17
6. Node Failures . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Node Failures . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Operation in an LDP environment . . . . . . . . . . . . . . . 18 7. Operation in an LDP environment . . . . . . . . . . . . . . . 19
8. Analysis of Real World Topologies . . . . . . . . . . . . . . 20 8. Analysis of Real World Topologies . . . . . . . . . . . . . . 20
8.1. Topology Details . . . . . . . . . . . . . . . . . . . . . 20 8.1. Topology Details . . . . . . . . . . . . . . . . . . . . 21
8.2. LFA only . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.2. LFA only . . . . . . . . . . . . . . . . . . . . . . . . 21
8.3. RLFA . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.3. RLFA . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.4. Comparison of LFA an RLFA results . . . . . . . . . . . . 23 8.4. Comparison of LFA an RLFA results . . . . . . . . . . . . 23
9. Management Considerations . . . . . . . . . . . . . . . . . . 24 9. Management Considerations . . . . . . . . . . . . . . . . . . 24
10. Historical Note . . . . . . . . . . . . . . . . . . . . . . . 24 10. Historical Note . . . . . . . . . . . . . . . . . . . . . . . 25
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
12. Security Considerations . . . . . . . . . . . . . . . . . . . 24 12. Security Considerations . . . . . . . . . . . . . . . . . . . 25
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
14. Informative References . . . . . . . . . . . . . . . . . . . . 25 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 14.1. Normative References . . . . . . . . . . . . . . . . . . 26
14.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Terminology 1. Terminology
This draft uses the terms defined in [RFC5714]. This section defines This draft uses the terms defined in [RFC5714]. This section defines
additional terms used in this draft. additional terms used in this draft.
Extended P-space
The union of the P-space of the neighbours of a
specific router with respect to the protected link
(see Section 4.2.1.2).
FIB Forwarding Information (data)Base. The database used FIB Forwarding Information (data)Base. The database used
by a packet forwarder to determine the actions it by a packet forwarder to determine the actions it
should take on a packet it is processing. should take on a packet it is processing.
Repair tunnel A tunnel established for the purpose of providing a
virtual neighbor which is a Loop Free Alternate.
P-space P-space is the set of routers reachable from a P-space P-space is the set of routers reachable from a
specific router using the normal FIB, without any path specific router using the normal FIB, without any path
(including equal cost path splits) transiting the (including equal cost path splits) transiting the
protected link. protected link.
For example, the P-space of S with respect to link For example, the P-space of S with respect to link
S-E, is the set of routers that S can reach without S-E, is the set of routers that S can reach without
using the protected link S-E. using the protected link S-E.
PQ node A node which is a member of both the P-space and the Extended P-space
Q-space. Where extended P-space is in use it is a
node which is a member of both the extended P-space The union of the P-space of the neighbours of a
and the Q-space. In remote LFA this is used as the specific router with respect to the protected link
repair tunnel endpoint. (see Section 4.2.1.2).
Q-space Q-space is the set of routers from which a specific Q-space Q-space is the set of routers from which a specific
router can be reached without any path (including router can be reached without any path (including
equal cost path splits) transiting the protected link. equal cost path splits) transiting the protected link.
Repair tunnel A tunnel established for the purpose of providing a PQ node A node which is a member of both the P-space and the
virtual neighbor which is a Loop Free Alternate. Q-space. Where extended P-space is in use it is a
node which is a member of both the extended P-space
and the Q-space. In remote LFA this is used as the
repair tunnel endpoint.
Remote LFA (RLFA) The use of a PQ node rather than a neighbour of Remote LFA (RLFA) The use of a PQ node rather than a neighbour of
the repairing node as the next hop in an LFA repair. the repairing node as the next hop in an LFA repair.
In this document we use the notation X-Y to mean the path from X to Y In this document we use the notation X-Y to mean the path from X to Y
over the link directly connecting X and Y, whilst the notation X->Y over the link directly connecting X and Y, whilst the notation X->Y
refers to the shortest path from X to Y via some set of unspecified refers to the shortest path from X to Y via some set of unspecified
nodes including the null set (i.e. including over a link directly nodes including the null set (i.e. including over a link directly
connecting X and Y). connecting X and Y).
2. Introduction 2. Introduction
RFC 5714 [RFC5714] describes a framework for IP Fast Re-route and RFC 5714 [RFC5714] describes a framework for IP Fast Re-route and
provides a summary of various proposed IPFRR solutions. A basic provides a summary of various proposed IPFRR solutions. A basic
mechanism using loop-free alternates (LFAs) is described in [RFC5286] mechanism using loop-free alternates (LFAs) is described in [RFC5286]
that provides good repair coverage in many topologies[RFC6571], that provides good repair coverage in many topologies [RFC6571],
especially those that are highly meshed. However, some topologies, especially those that are highly meshed. However, some topologies,
notably ring based topologies are not well protected by LFAs alone. notably ring based topologies are not well protected by LFAs alone.
This is illustrated in Figure 1 below. This is illustrated in Figure 1 below.
S---E S---E
/ \ / \
A D A D
\ / \ /
B---C B---C
skipping to change at page 4, line 32 skipping to change at page 4, line 32
If all link costs are equal, the link S-E cannot be fully protected If all link costs are equal, the link S-E cannot be fully protected
by LFAs. The destination C is an ECMP from S, and so can be by LFAs. The destination C is an ECMP from S, and so can be
protected when S-E fails, but D and E are not protectable using LFAs. protected when S-E fails, but D and E are not protectable using LFAs.
This draft describes extensions to the basic repair mechanism in This draft describes extensions to the basic repair mechanism in
which tunnels are used to provide additional logical links which can which tunnels are used to provide additional logical links which can
then be used as loop free alternates where none exist in the original then be used as loop free alternates where none exist in the original
topology. In Figure 1 S can reach A, B, and C without going via E; topology. In Figure 1 S can reach A, B, and C without going via E;
these form S's extended P-space. The routers that can reach E these form S's extended P-space. The routers that can reach E
without going through S-E will be E's Q-space; these are D and C. B without going through S-E will be E's Q-space; these are D and C. B
has equal-cost paths via B-A-S-E and B-C-D-E and so may go through has equal-cost paths via B-A-S-E and B-C-D-E and so may go through
S-E. The single node in both S's P-space and E's Q-space is C; thus S-E. The single node in both S's P-space and E's Q-space is C; thus
node C is selected as the repair tunnel's end-point. Thus, if a node C is selected as the repair tunnel's end-point. Thus, if a
tunnel is provided between S and C as shown in Figure 2 then C, now tunnel is provided between S and C as shown in Figure 2 then C, now
being a direct neighbor of S would become an LFA for D and E. The being a direct neighbor of S would become an LFA for D and E. The
definition of (extended-)P space and Q space are provided in definition of (extended-)P space and Q space are provided in
Section 1 and details of the calculation of the tunnel end points is Section 1 and details of the calculation of the tunnel end points is
provided in Section 4.2. provided in Section 4.2.
The non-failure traffic distribution is not disrupted by the The non-failure traffic distribution is not disrupted by the
provision of such a tunnel since it is only used for repair traffic provision of such a tunnel since it is only used for repair traffic
and MUST NOT be used for normal traffic. and MUST NOT be used for normal traffic.
S---E S---E
/ \ \ / \ \
skipping to change at page 5, line 20 skipping to change at page 5, line 27
provided in Section 8, and a side by side comparison between LFA and provided in Section 8, and a side by side comparison between LFA and
remote LFA is provided in Section 8.4. remote LFA is provided in Section 8.4.
Remote LFA is suitable for incremental deployment within a network, Remote LFA is suitable for incremental deployment within a network,
including a network that is already deploying LFA. Computation of including a network that is already deploying LFA. Computation of
the repair path requires acceptable CPU resources, and takes place the repair path requires acceptable CPU resources, and takes place
exclusively on the repairing node. In MPLS networks the targeted LDP exclusively on the repairing node. In MPLS networks the targeted LDP
protocol needed to learn the label binding at the repair tunnel protocol needed to learn the label binding at the repair tunnel
endpoint is a well understood and widely deployed technology. endpoint is a well understood and widely deployed technology.
This technique describes in this document is directed at providing The technique described in this document is directed at providing
repairs in the case of link failures. Considerations regarding node repairs in the case of link failures. Considerations regarding node
failures are discussed in Section 6. This memo describes a solution failures are discussed in Section 6. This memo describes a solution
to the case where the failure occurs on a point to point link. It to the case where the failure occurs on a point to point link. It
covers the case where the repair first hop is reached via a broadcast covers the case where the repair first hop is reached via a broadcast
or non-broadcast multi-access (NBMA) link such as a LAN, and the case or non-broadcast multi-access (NBMA) link such as a LAN, and the case
where the P or Q node is attached via such a link. It does not where the P or Q node is attached via such a link. It does not
however cover the more complicated case where the failed interface is however cover the more complicated case where the failed interface is
a broadcast or non-broadcast multi-access (NBMA) link. a broadcast or non-broadcast multi-access (NBMA) link.
This document considers the case when the repair path is confined to This document considers the case when the repair path is confined to
skipping to change at page 6, line 6 skipping to change at page 6, line 11
A tunneled repair path tunnels traffic to some staging point in the A tunneled repair path tunnels traffic to some staging point in the
network from which it is known that, in the absence of a worse than network from which it is known that, in the absence of a worse than
anticipated failure, the traffic will travel to its destination using anticipated failure, the traffic will travel to its destination using
normal forwarding without looping back. This is equivalent to normal forwarding without looping back. This is equivalent to
providing a virtual loop-free alternate to supplement the physical providing a virtual loop-free alternate to supplement the physical
loop-free alternates. Hence the name "Remote LFA FRR". In its loop-free alternates. Hence the name "Remote LFA FRR". In its
simplest form, when a link cannot be entirely protected with local simplest form, when a link cannot be entirely protected with local
LFA neighbors, the protecting router seeks the help of a remote LFA LFA neighbors, the protecting router seeks the help of a remote LFA
staging point. Network manageability considerations may lead to a staging point. Network manageability considerations may lead to a
repair strategy that uses a remote LFA more frequently repair strategy that uses a remote LFA more frequently
[I-D.ietf-rtgwg-lfa-manageability].] [I-D.ietf-rtgwg-lfa-manageability].
Examples of worse failures are node failures (see Section 6 ), and Examples of worse failures are node failures (see Section 6 ), and
through the failure of a shared risk link group (SRLG), the through through the failure of a shared risk link group (SRLG), the through
the independent concurrent failure of multiple links, and these are the independent concurrent failure of multiple links, and these are
out of scope for this specification. out of scope for this specification.
3.1. Tunnels as Repair Paths 3.1. Tunnels as Repair Paths
Consider an arbitrary protected link S-E. In LFA FRR, if a path to Consider an arbitrary protected link S-E. In LFA FRR, if a path to
the destination from a neighbor N of S does not cause a packet to the destination from a neighbor N of S does not cause a packet to
loop back over the link S-E (i.e. N is a loop-free alternate), then loop back over the link S-E (i.e. N is a loop-free alternate), then
S can send the packet to N and the packet will be delivered to the S can send the packet to N and the packet will be delivered to the
destination using the pre-failure forwarding information. If there destination using the pre-failure forwarding information. If there
is no such LFA neighbor, then S may be able to create a virtual LFA is no such LFA neighbor, then S may be able to create a virtual LFA
by using a tunnel to carry the packet to a point in the network which by using a tunnel to carry the packet to a point in the network which
is not a direct neighbor of S from which the packet will be delivered is not a direct neighbor of S from which the packet will be delivered
to the destination without looping back to S. In this document such a to the destination without looping back to S. In this document such
tunnel is termed a repair tunnel. The tail-end of this tunnel (the a tunnel is termed a repair tunnel. The tail-end of this tunnel (the
repair tunnel endpoint) is a "PQ node" and the repair mechanism is a repair tunnel endpoint) is a "PQ node" and the repair mechanism is a
"remote LFA". This tunnel MUST NOT traverse the link S-E. "remote LFA". This tunnel MUST NOT traverse the link S-E.
Note that the repair tunnel terminates at some intermediate router Note that the repair tunnel terminates at some intermediate router
between S and E, and not E itself. This is clearly the case, since between S and E, and not E itself. This is clearly the case, since
if it were possible to construct a tunnel from S to E then a if it were possible to construct a tunnel from S to E then a
conventional LFA would have been sufficient to effect the repair. conventional LFA would have been sufficient to effect the repair.
3.2. Tunnel Requirements 3.2. Tunnel Requirements
skipping to change at page 8, line 8 skipping to change at page 8, line 16
The repair tunnel endpoint needs to be a node in the network The repair tunnel endpoint needs to be a node in the network
reachable from S without traversing S-E. In addition, the repair reachable from S without traversing S-E. In addition, the repair
tunnel end point needs to be a node from which packets will normally tunnel end point needs to be a node from which packets will normally
flow towards their destination without being attracted back to the flow towards their destination without being attracted back to the
failed link S-E. failed link S-E.
Note that once released from the tunnel, the packet will be Note that once released from the tunnel, the packet will be
forwarded, as normal, on the shortest path from the release point to forwarded, as normal, on the shortest path from the release point to
its destination. This may result in the packet traversing the router its destination. This may result in the packet traversing the router
E at the far end of the protected link S-E., but this is obviously E at the far end of the protected link S-E, but this is obviously not
not required. required.
The properties that are required of repair tunnel end points are The properties that are required of repair tunnel end points are
therefore: therefore:
o The repair tunneled point MUST be reachable from the tunnel source o The repair tunneled point MUST be reachable from the tunnel source
without traversing the failed link; and without traversing the failed link; and
o When released, tunneled packets MUST proceed towards their o When released from the tunnel, packets MUST proceed towards their
destination without being attracted back over the failed link. destination without being attracted back over the failed link.
Provided both these requirements are met, packets forwarded over the Provided both these requirements are met, packets forwarded over the
repair tunnel will reach their destination and will not loop. repair tunnel will reach their destination and will not loop.
In some topologies it will not be possible to find a repair tunnel In some topologies it will not be possible to find a repair tunnel
endpoint that exhibits both the required properties. For example if endpoint that exhibits both the required properties. For example if
the ring topology illustrated in Figure 1 had a cost of 4 for the the ring topology illustrated in Figure 1 had a cost of 4 for the
link B-C, while the remaining links were cost 1, then it would not be link B-C, while the remaining links were cost 1, then it would not be
possible to establish a tunnel from S to C (without resorting to some possible to establish a tunnel from S to C (without resorting to some
skipping to change at page 8, line 51 skipping to change at page 9, line 10
this the S's P-space with respect to the failure of link S-E. this the S's P-space with respect to the failure of link S-E.
o We show how to extend the distance of the tunnel endpoint from the o We show how to extend the distance of the tunnel endpoint from the
point of local repair (PLR) by noting that S is able to use the point of local repair (PLR) by noting that S is able to use the
P-Space of its neighbours since S can determine which neighbour it P-Space of its neighbours since S can determine which neighbour it
will use as the next hop for the repair. We call this the S's will use as the next hop for the repair. We call this the S's
Extended P-Space with respect to the failure of link S-E. The use Extended P-Space with respect to the failure of link S-E. The use
of extended P-Space allows greater repair coverage and is the of extended P-Space allows greater repair coverage and is the
preferred approach. preferred approach.
o Finally we how to compute the set of routers from which the node E o Finally we show how to compute the set of routers from which the
can be reached, by normal forwarding, without traversing the link node E can be reached, by normal forwarding, without traversing
S-E. This is called the Q-space of E with respect to the link the link S-E. This is called the Q-space of E with respect to the
S-E. link S-E.
The selection of the preferred node from the set of nodes that an in The selection of the preferred node from the set of nodes that an in
both Extended P-Space and Q-Space is described in Section 4.2.2. both Extended P-Space and Q-Space is described in Section 4.2.2.
A suitable cost based algorithm to compute the set of nodes common to A suitable cost based algorithm to compute the set of nodes common to
both extended P-space and Q-space is provide in Section 4.3. both extended P-space and Q-space is provided in Section 4.3.
4.2.1.1. P-space 4.2.1.1. P-space
The set of routers which can be reached from S on the shortest path The set of routers which can be reached from S on the shortest path
tree without traversing S-E is termed the P-space of S with respect tree without traversing S-E is termed the P-space of S with respect
to the link S-E. The P-space can be obtained by computing a shortest to the link S-E. The P-space can be obtained by computing a shortest
path tree (SPT) rooted at S and excising the sub-tree reached via the path tree (SPT) rooted at S and excising the sub-tree reached via the
link S-E (including those routers which are members of an ECMP that link S-E (including those routers which are members of an ECMP that
includes link S-E). The exclusion of routers reachable via an ECMP includes link S-E). The exclusion of routers reachable via an ECMP
that includes S-E prevents the forwarding subsystem attempting to a that includes S-E prevents the forwarding subsystem attempting to a
skipping to change at page 9, line 40 skipping to change at page 9, line 48
4.2.1.2. Extended P-space 4.2.1.2. Extended P-space
The description in Section 4.2.1.1 calculated router S's P-space The description in Section 4.2.1.1 calculated router S's P-space
rooted at S itself. However, since router S will only use a repair rooted at S itself. However, since router S will only use a repair
path when it has detected the failure of the link S-E, the initial path when it has detected the failure of the link S-E, the initial
hop of the repair path need not be subject to S's normal forwarding hop of the repair path need not be subject to S's normal forwarding
decision process. Thus we introduce the concept of extended P-space. decision process. Thus we introduce the concept of extended P-space.
Router S's extended P-space is the union of the P-spaces of each of Router S's extended P-space is the union of the P-spaces of each of
S's neighbours (N). This may be calculated by computing an SPT at S's neighbours (N). This may be calculated by computing an SPT at
each of S's neighbors (excluding E) and excising the subtree reached each of S's neighbors (excluding E) and excising the subtree reached
via the path N->S->E. The use of extended P-space may allow router S via the path N->S->E. The use of extended P-space may allow router S
to reach potential repair tunnel end points that were otherwise to reach potential repair tunnel end points that were otherwise
unreachable. In cost terms a router (P) is in extended P-space if unreachable. In cost terms a router (P) is in extended P-space if
the shortest path cost N->P is strictly less than the shortest path the shortest path cost N->P is strictly less than the shortest path
cost N->S->E->P. In other words, once the packet it forced to N by S, cost N->S->E->P. In other words, once the packet it forced to N by
it is lower cost for it to continue on to P by any path except one S, it is lower cost for it to continue on to P by any path except one
that takes it back to S and then across the S->E link. that takes it back to S and then across the S->E link.
Since in the case of Figure 1 node A is a per-prefix LFA for the Since in the case of Figure 1 node A is a per-prefix LFA for the
destination node C, the set of extended P-space nodes comprises nodes destination node C, the set of extended P-space nodes comprises nodes
A, B and C. Since node C is also in E's Q-space, there is now a node A, B and C. Since node C is also in E's Q-space, there is now a node
common to both extended P-space and Q-space which can be used as a common to both extended P-space and Q-space which can be used as a
repair tunnel end-point to protect the link S-E. repair tunnel end-point to protect the link S-E.
4.2.1.3. Q-space 4.2.1.3. Q-space
The set of routers from which the node E can be reached, by normal The set of routers from which the node E can be reached, by normal
forwarding, without traversing the link S-E is termed the Q-space of forwarding, without traversing the link S-E is termed the Q-space of
E with respect to the link S-E. The Q-space can be obtained by E with respect to the link S-E. The Q-space can be obtained by
computing a reverse shortest path tree (rSPT) rooted at E, with the computing a reverse shortest path tree (rSPT) rooted at E, with the
sub-tree which traverses the failed link excised (including those sub-tree which traverses the failed link excised (including those
which are members of an ECMP). The rSPT uses the cost towards the which are members of an ECMP). The rSPT uses the cost towards the
root rather than from it and yields the best paths towards the root root rather than from it and yields the best paths towards the root
from other nodes in the network. In the case of Figure 1 the Q-space from other nodes in the network. In the case of Figure 1 the Q-space
comprises nodes C and D only. Expressed in cost terms the set of comprises nodes C and D only. Expressed in cost terms the set of
routers {Q} are those for which the shortest path cost Q->E is routers {Q} are those for which the shortest path cost Q<-E is
strictly less than the shortest path cost Q->S->E. In Figure 1 the strictly less than the shortest path cost Q<-S<-E. In Figure 1 the
intersection of the E's Q-space with S's P-space defines the set of intersection of the E's Q-space with S's P-space defines the set of
viable repair tunnel end-points, known as "PQ nodes". As can be viable repair tunnel end-points, known as "PQ nodes". As can be
seen, for the case of Figure 1 there is no common node and hence no seen, for the case of Figure 1 there is no common node and hence no
viable repair tunnel end-point. viable repair tunnel end-point. However when the extended the
extended P-space Section 4.2.1.2 at S is considered a suitable
intersection is found at C.
Note that the Q-space calculation could be conducted for each Note that the Q-space calculation could be conducted for each
individual destination and a per-destination repair tunnel end point individual destination and a per-destination repair tunnel end point
determined. However this would, in the worst case, require an SPF determined. However this would, in the worst case, require an SPF
computation per destination which is not currently considered to be computation per destination which is not currently considered to be
scalable. We therefore use the Q-space of E as a proxy for the scalable. We therefore use the Q-space of E as a proxy for the
Q-space of each destination. This approximation is obviously correct Q-space of each destination. This approximation is obviously correct
since the repair is only used for the set of destinations which were, since the repair is only used for the set of destinations which were,
prior to the failure, routed through node E. This is analogous to the prior to the failure, routed through node E. This is analogous to
use of link-LFAs rather than per-prefix LFAs. the use of link-LFAs rather than per-prefix LFAs.
4.2.2. Selecting Repair Paths 4.2.2. Selecting Repair Paths
The mechanisms described above will identify all the possible repair The mechanisms described above will identify all the possible repair
tunnel end points that can be used to protect a particular link. In tunnel end points that can be used to protect a particular link. In
a well-connected network there are likely to be multiple possible a well-connected network there are likely to be multiple possible
release points for each protected link. All will deliver the packets release points for each protected link. All will deliver the packets
correctly so, arguably, it does not matter which is chosen. However, correctly so, arguably, it does not matter which is chosen. However,
one repair tunnel end point may be preferred over the others on the one repair tunnel end point may be preferred over the others on the
basis of path cost or some other selection criteria. basis of path cost or some other selection criteria.
There is no technical requirement for the selection criteria to be There is no technical requirement for the selection criteria to be
consistent across all routers, but such consistency may be desirable consistent across all routers, but such consistency may be desirable
from an operational point of view. In general there are advantages from an operational point of view. In general there are advantages
in choosing the repair tunnel end point closest (shortest metric) to in choosing the repair tunnel end point closest (shortest metric) to
S. Choosing the closest maximises the opportunity for the traffic to S. Choosing the closest maximises the opportunity for the traffic to
be load balanced once it has been released from the tunnel. For be load balanced once it has been released from the tunnel. For
consistency in behavior, it is RECOMMENDED that member of the set of consistency in behavior, it is RECOMMENDED that the member of the set
routers {PQ} with the lowest cost S->P be the default choice for P. of routers {PQ} with the lowest cost S->P be the default choice for
P. In the event of a tie the router with the lowest node identifier
In the event of a tie the router with the lowest node identifier
SHOULD be selected. SHOULD be selected.
It is a local matter whether the repair path selection policy used by It is a local matter whether the repair path selection policy used by
the router favours LFA repairs over RLFA repairs. An LFA repair has the router favours LFA repairs over RLFA repairs. An LFA repair has
the advantage of not requiring the use of tunnel, however network the advantage of not requiring the use of tunnel, however network
manageability considerations may lead to a repair strategy that uses manageability considerations may lead to a repair strategy that uses
a remote LFA more frequently [I-D.ietf-rtgwg-lfa-manageability]. a remote LFA more frequently [I-D.ietf-rtgwg-lfa-manageability].
As described in [RFC5286], always selecting a PQ node that is As described in [RFC5286], always selecting a PQ node that is
downstream with respect to the repairing node, prevents the formation downstream with respect to the repairing node, prevents the formation
skipping to change at page 11, line 27 skipping to change at page 11, line 37
downstream nodes reduces the repair coverage, and operators are downstream nodes reduces the repair coverage, and operators are
advised to determine whether adequate coverage is achieved before advised to determine whether adequate coverage is achieved before
enabling this selection feature. enabling this selection feature.
4.3. A Cost Based RLFA Algorithm 4.3. A Cost Based RLFA Algorithm
The preceding text has mostly described the computation of the remote The preceding text has mostly described the computation of the remote
LFA repair target (PQ) in terms of the intersection of two LFA repair target (PQ) in terms of the intersection of two
reachability graphs computed using SPFs. This section describes a reachability graphs computed using SPFs. This section describes a
method of computing the remote LFA repair target for a specific method of computing the remote LFA repair target for a specific
failed link using a cost based algorithm. The pseudo-code provides failed link using a cost based algorithm. The pseudo-code provided
in this section avoids unnecessary SPF computations, but for the sake in this section avoids unnecessary SPF computations, but for the sake
of readability, it does not otherwise try to optimize the code. The of readability, it does not otherwise try to optimize the code. The
algorithm covers the case where the repair first hop is reached via a algorithm covers the case where the repair first hop is reached via a
broadcast or non-broadcast multi-access (NBMA) link such as a LAN. broadcast or non-broadcast multi-access (NBMA) link such as a LAN.
It also covers the case where the P or Q node is attached via such a It also covers the case where the P or Q node is attached via such a
link. It does not cover the case where the failed interface is a link. It does not cover the case where the failed interface is a
broadcast or non-broadcast multi-access (NBMA) link. To address that broadcast or non-broadcast multi-access (NBMA) link. To address that
case it is necessary to compute the Q space of each neighbor of the case it is necessary to compute the Q space of each neighbor of the
repairing router reachable though the LAN, i.e. to treat the repairing router reachable though the LAN, i.e. to treat the
pseudonode as a node failure. This is because the Q spaces of the pseudonode as a node failure. This is because the Q spaces of the
skipping to change at page 16, line 38 skipping to change at page 16, line 38
if (y.valid_tunnel_endpoint) if (y.valid_tunnel_endpoint)
Compute_and_Store_Forward_SPF(y) Compute_and_Store_Forward_SPF(y)
if ((D_opt(y,dest) < D_opt(self,dest)) if ((D_opt(y,dest) < D_opt(self,dest))
y.valid_tunnel_endpoint = true y.valid_tunnel_endpoint = true
else else
y.valid_tunnel_endpoint = false y.valid_tunnel_endpoint = false
// //
///////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////////////
4.4. Interactions with IS-IS Overload, RFC 3137, and Costed Out Links 4.4. Interactions with IS-IS Overload, RFC 3137, and Costed Out Links
The consideration concerning interactions with IS-IS Overload, Since normal link state routing takes into account the IS-IS overload
[RFC3137], and costed out links as described in [RFC5286] apply. In bit, [RFC6987], and costing out of links as described in [RFC5286],
selecting a PQ node a PLR MUST exclude any candidate that is the forward SPFs performed by the PLR rooted at the neighbors of the
reachable (including via ECMP) from the PLR via a path subject to one PLR also need to take this into account. A repair tunnel path from a
of the above exclusions. The method of determining the exclusion is neighbor of the PLR to a repair tunnel endpoint will generally avoid
a local matter. the nodes and links excluded by the IGP overload/costing out rules.
However, there are two situations where this behavior may result in a
repair path traversing a link or router that should be excluded:
1. When the first hop on the repair tunnel path (from the PLR to a
direct neighbor) does not follow the IGP shortest path. In this
case, the PLR MUST NOT use a repair tunnel path whose first hop
is along a link whose cost or reverse cost is LSInfinity (for
OSPF) or the maximum cost (for IS-IS) or, has the overload bit
set (for IS-IS).
2. The IS-IS overload bit and the mechanism of [RFC6987] only
prevent transit traffic from traversing a node. They do not
prevent traffic destined to a node. The per-neighbor forwards
SPFs using the standard IGP overload rules will not prevent a PLR
from choosing a repair tunnel endpoint that is advertising a
desire to not carry transit traffic. Therefore, the PLR MUST NOT
use a repair tunnel endpoint with the IS-IS overload bit set, or
where all outgoing interfaces have the cost set to LSInfinity for
OSPF.
5. Example Application of Remote LFAs 5. Example Application of Remote LFAs
An example of a commonly deployed topology which is not fully An example of a commonly deployed topology which is not fully
protected by LFAs alone is shown in Figure 3. PE1 and PE2 are protected by LFAs alone is shown in Figure 3. PE1 and PE2 are
connected in the same site. P1 and P2 may be geographically connected in the same site. P1 and P2 may be geographically
separated (inter-site). In order to guarantee the lowest latency separated (inter-site). In order to guarantee the lowest latency
path from/to all other remote PEs, normally the shortest path follows path from/to all other remote PEs, normally the shortest path follows
the geographical distance of the site locations. Therefore, to the geographical distance of the site locations. Therefore, to
ensure this, a lower IGP metric (5) is assigned between PE1 and PE2. ensure this, a lower IGP metric (5) is assigned between PE1 and PE2.
A high metric (1000) is set on the P-PE links to prevent the PEs A high metric (1000) is set on the P-PE links to prevent the PEs
being used for transit traffic. The PEs are not individually dual- being used for transit traffic. The PEs are not individually dual-
homed in order to reduce costs. homed in order to reduce costs.
This is a common topology in SP networks. This is a common topology in SP networks.
When a failure occurs on the link between PE1 and P2, PE1 does not When a failure occurs on the link between PE1 and P1, PE1 does not
have an LFA for traffic reachable via P1. Similarly, by symmetry, if have an LFA for traffic reachable via P1. Similarly, by symmetry, if
the link between PE2 and P1 fails, PE2 does not have an LFA for the link between PE2 and P2 fails, PE2 does not have an LFA for
traffic reachable via P2. traffic reachable via P2.
Increasing the metric between PE1 and PE2 to allow the LFA would Increasing the metric between PE1 and PE2 to allow the LFA would
impact the normal traffic performance by potentially increasing the impact the normal traffic performance by potentially increasing the
latency. latency.
| 100 |
-P1---------P2- | 100 |
\ / -P1---------P2-
1000 \ / 1000 \ /
PE1---PE2 1000 \ / 1000
5 PE1---PE2
5
Figure 3: Example SP topology Figure 3: Example SP topology
Clearly, full protection can be provided, using the techniques Clearly, full protection can be provided, using the techniques
described in this draft, by PE1 choosing P1 as the remote LFA repair described in this draft, by PE1 choosing P2 as the remote LFA repair
target node, and PE2 choosing P2 as the remote LFA repair target. target node, and PE2 choosing P1 as the remote LFA repair target.
6. Node Failures 6. Node Failures
When the failure is a node failure rather than a link failure there When the failure is a node failure rather than a link failure there
is a danger that the RLFA repair will loop. This is discussed in is a danger that the RLFA repair will loop. This is discussed in
detail in [I-D.bryant-ipfrr-tunnels]. In summary problem is that two detail in [I-D.bryant-ipfrr-tunnels]. In summary the problem is that
of more of E's neighbors each with E as the next hop to some two of more of E's neighbors each with E as the next hop to some
destination D may attempt to repair a packet addressed to destination destination D may attempt to repair a packet addressed to destination
D via the other neighbor and then E, thus causing a loop to form. A D via the other neighbor and then E, thus causing a loop to form. A
similar problem exists in the case of a shared risk link group similar problem exists in the case of a shared risk link group
failure where the PLR for each failure attempts to repair via the failure where the PLR for each failure attempts to repair via the
other failure. As will be noted from [I-D.bryant-ipfrr-tunnels], other failure. As will be noted from [I-D.bryant-ipfrr-tunnels],
this can rapidly become a complex problem to address. this can rapidly become a complex problem to address.
There are a number of ways to minimize the probability of a loop There are a number of ways to minimize the probability of a loop
forming when a node failure occurs and there exists the possibility forming when a node failure occurs and there exists the possibility
that two of E's neighbors may form a mutual repair. that two of E's neighbors may form a mutual repair.
skipping to change at page 18, line 33 skipping to change at page 19, line 11
the repairing node). This means that some neighbor of E (X) can the repairing node). This means that some neighbor of E (X) can
repair via some other neighbor of E (Y), but Y cannot repair via repair via some other neighbor of E (Y), but Y cannot repair via
X. X.
Case 1 accepts that loops may form and suppresses them by dropping Case 1 accepts that loops may form and suppresses them by dropping
packets. Dropping packets may be considered less detrimental than packets. Dropping packets may be considered less detrimental than
looping packets. This approach may also lead to dropping some looping packets. This approach may also lead to dropping some
legitimate packets. Cases 2 and 3 above prevent the formation of a legitimate packets. Cases 2 and 3 above prevent the formation of a
loop, but at the expense of a reduced repair coverage and at the cost loop, but at the expense of a reduced repair coverage and at the cost
of additional complexity in the algorithm to compute the repair path. of additional complexity in the algorithm to compute the repair path.
Alternatively one might choose to assume that the probability of a
node failure and microloops forming is sufficiently rare that the
case can be ignored.
The probability of a node failure and the consequences of node The probability of a node failure and the consequences of node
failure in any particular topology will depend on the node design, failure in any particular topology will depend on the node design,
the particular topology in use, and node failure strategy (including the particular topology in use, and the strategy adopted under node
the null strategy). It is recommended that a network operator failure. It is recommended that a network operator perform an
perform an analysis of the consequences and probability of node analysis of the consequences and probability of node failure in their
failure in their network, and determine whether the incidence and network, and determine whether the incidence and consequence of
consequence of occurrence are acceptable. occurrence are acceptable.
This topic is further discussed in This topic is further discussed in
[I-D.psarkar-rtgwg-rlfa-node-protection]. [I-D.psarkar-rtgwg-rlfa-node-protection].
7. Operation in an LDP environment 7. Operation in an LDP environment
Where this technique is used in an MPLS network using LDP [RFC5036], Where this technique is used in an MPLS network using LDP [RFC5036],
and S is a transit node, S will need to swap the top label in the and S is a transit node, S will need to swap the top label in the
stack for the emote LFA repair target's (PQ's) label to the stack for the remote LFA repair target's (PQ's) label to the
destination, and to then push its own label for the remote LFA repair destination, and to then push its own label for the remote LFA repair
target. target.
In the example Figure 2 S already has the first hop (A) label for the In the example Figure 2 S already has the first hop (A) label for the
remote LFA repair target (C) as a result of the ordinary operation of remote LFA repair target (C) as a result of the ordinary operation of
LDP. To get the remote LFA repair target's label (C's label) for the LDP. To get the remote LFA repair target's label (C's label) for the
destination (D), S needs to establish a targeted LDP session with C. destination (D), S needs to establish a targeted LDP session with C.
The label stack for normal operation and RLFA operation is shown The label stack for normal operation and RLFA operation is shown
below in Figure 4. below in Figure 4.
+-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+
| datalink | | datalink | | datalink | | datalink | | datalink | | datalink |
+-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+
| S's label for D | | E's label for D | | A's label for C | | S's label for D | | E's label for D | | A's label for C |
+-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+
| Payload | | Payload | | C's label for D | | Payload | | Payload | | C's label for D |
+-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+
X Y | Payload | X Y | Payload |
+-----------------+ +-----------------+
Z Z
skipping to change at page 21, line 52 skipping to change at page 22, line 42
+------+--------+---------+ +------+--------+---------+
8.3. RLFA 8.3. RLFA
The figure below shows the percentage of protected destinations (% The figure below shows the percentage of protected destinations (%
prot) and % guaranteed node protected destinations ( % gtd N) for prot) and % guaranteed node protected destinations ( % gtd N) for
RLFA protection in the topologies studies. In addition, it show the RLFA protection in the topologies studies. In addition, it show the
percentage of destinations using an RLFA repair (% PQ) together with percentage of destinations using an RLFA repair (% PQ) together with
the total number of unidirectional RLFA targeted LDP session the total number of unidirectional RLFA targeted LDP session
established (# PQ), the number of PQ sessions which would be required established (# PQ), the number of PQ sessions which would be required
for complete protection, but which could not be established (no PQ). for complete protection, but which could not be established because
there was no PQ node, i.e. the number of cases whether neither LFA or
It also shows the 50 (p50), 90 (p90) and 100 (p100) percentiles for RLFA protection was possible (no PQ). It also shows the 50 (p50), 90
the number of individual LDP sessions terminating at an individual (p90) and 100 (p100) percentiles for the number of individual LDP
node (whether used for TX, RX or both). sessions terminating at an individual node (whether used for TX, RX
or both).
For example, if there were LDP sessions required A->B, A->C, C->A, For example, if there were LDP sessions required A->B, A->C, C->A,
C->D, these would be counted as 2, 1, 2, 1 at nodes A,B,C and D C->D, these would be counted as 2, 1, 2, 1 at nodes A,B,C and D
respectively because:- respectively because:-
A has two sessions (to nodes B and C) A has two sessions (to nodes B and C)
B has one session (to node A) B has one session (to node A)
C has two sessions (to nodes A and D) C has two sessions (to nodes A and D)
D has one session (to node D) D has one session (to node D)
In this study, remote LFA is only used when necessary. i.e. when In this study, remote LFA is only used when necessary. i.e. when
there is at least one destination which is not reparable by a per there is at least one destination which is not reparable by a per
destination LFA, and a single remote LFA tunnel is used (if destination LFA, and a single remote LFA tunnel is used (if
available) to repair traffic to all such destinations. The remote available) to repair traffic to all such destinations. The remote
LFA repair target points are computed using extended P space and LFA repair target points are computed using extended P space and
choosing the PQ node which has the lowest metric cost from the choosing the PQ node which has the lowest metric cost from the
repairing node. repairing node.
+------+--------+--------+------+------+-------+-----+-----+------+ +------+--------+--------+------+------+-------+-----+-----+------+
| topo | % prot |% gtd N | % PQ | # PQ | no PQ | p50 | p90 | p100 | | topo | % prot |% gtd N | % PQ | # PQ | no PQ | p50 | p90 | p100 |
+------+--------+--------+------+------+-------+-----+-----+------+ +------+--------+--------+------+------+-------+-----+-----+------+
skipping to change at page 23, line 38 skipping to change at page 24, line 30
| 12 | 99.5 | 99.999 | 62.4 | 62.8 | | 12 | 99.5 | 99.999 | 62.4 | 62.8 |
| 13 | 92.4 | 97.5 | 51.6 | 54.6 | | 13 | 92.4 | 97.5 | 51.6 | 54.6 |
| 14 | 99.3 |100 | 48.6 | 48.6 | | 14 | 99.3 |100 | 48.6 | 48.6 |
+------+--------+--------+---------+---------+ +------+--------+--------+---------+---------+
As shown in the table, remote LFA provides close to 100% prefix As shown in the table, remote LFA provides close to 100% prefix
protection against link failure in 11 of the 14 topologies studied, protection against link failure in 11 of the 14 topologies studied,
and provides a significant improvement in two of the remaining three and provides a significant improvement in two of the remaining three
cases. In an MPLS network, this is achieved without any scaleability cases. In an MPLS network, this is achieved without any scaleability
impact, as the tunnels to the PQ nodes are always present as a impact, as the tunnels to the PQ nodes are always present as a
property of an LDP-based deployment. In the very few cases where P property of an LDP-based deployment.
and Q spaces have an empty intersection, a possible solution is to
select the closest node in the Q space and signal an explicitly- In the small number of cases where there is no intersection between
routed RSVP TE LSP to that Q node. A targeted LDP session is then the (extended)P-space and the Q-space, a number of solutions to
established with the selected Q node and the rest of the solution is providing a suitable path between such disjoint regions in the
identical to that described elsewhere in this document. network have been discussed in the working group. For example an
Alternatively the segment routing technology being defined in the explicitly routed LSP between P and Q might be set up using RSVP-TE
IETF may be used to carry the traffic between non-collocated P and Q or using Segment Routing [I-D.filsfils-rtgwg-segment-routing]. Such
nodes [I-D.filsfils-rtgwg-segment-routing-use-cases], extended repair methods are outside the scope of this document.
[I-D.filsfils-rtgwg-segment-routing],
[I-D.gredler-rtgwg-igp-label-advertisement].
9. Management Considerations 9. Management Considerations
The management of LFA and remote LFA is the subject of ongoing work The management of LFA and remote LFA is the subject of ongoing work
withing the IETF[I-D.ietf-rtgwg-lfa-manageability] to which the withing the IETF [I-D.ietf-rtgwg-lfa-manageability] to which the
reader is referred. Management considerations may lead to a reader is referred. Management considerations may lead to a
preference for the use of a remote LFA over an available LFA. This preference for the use of a remote LFA over an available LFA. This
preference is a matter for the network operator, and not a matter of preference is a matter for the network operator, and not a matter of
protocol correctness. protocol correctness.
10. Historical Note 10. Historical Note
The basic concepts behind Remote LFA were invented in 2002 and were The basic concepts behind Remote LFA were invented in 2002 and were
later included in [I-D.bryant-ipfrr-tunnels], submitted in 2004. later included in [I-D.bryant-ipfrr-tunnels], submitted in 2004.
skipping to change at page 24, line 34 skipping to change at page 25, line 25
As explained in [RFC6571], the purpose of the LFA FRR technology is As explained in [RFC6571], the purpose of the LFA FRR technology is
not to provide coverage at any cost. A solution for this already not to provide coverage at any cost. A solution for this already
exists with MPLS TE FRR. MPLS TE FRR is a mature technology which is exists with MPLS TE FRR. MPLS TE FRR is a mature technology which is
able to provide protection in any topology thanks to the explicit able to provide protection in any topology thanks to the explicit
routing capability of MPLS TE. routing capability of MPLS TE.
The purpose of LFA FRR technology is to provide for a simple FRR The purpose of LFA FRR technology is to provide for a simple FRR
solution when such a solution is possible. The first step along this solution when such a solution is possible. The first step along this
simplicity approach was "local" LFA [RFC5286]. We propose "Remote simplicity approach was "local" LFA [RFC5286]. We propose "Remote
LFA" as a natural second step. The following section motivates its LFA" as a natural second step.
benefits in terms of simplicity, incremental deployment and
significant coverage increase.
11. IANA Considerations 11. IANA Considerations
There are no IANA considerations that arise from this architectural There are no IANA considerations that arise from this architectural
description of IPFRR. The RFC Editor may remove this section on description of IPFRR. The RFC Editor may remove this section on
publication. publication.
12. Security Considerations 12. Security Considerations
The security considerations of RFC 5286 also apply. The security considerations of RFC 5286 also apply.
To prevent their use as an attack vector the repair tunnel endpoints To prevent their use as an attack vector the repair tunnel endpoints
SHOULD be assigned from a set of addresses that are not reachable SHOULD be assigned from a set of addresses that are not reachable
from outside the routing domain. from outside the routing domain.
13. Acknowledgments 13. Acknowledgments
The authors wish to thank Levente Csikor and Chris Bowers for their The authors wish to thank Levente Csikor and Chris Bowers for their
contribution to the cost based algorithm text. We thank Alia Atlas, contribution to the cost based algorithm text. We thank Alia Atlas,
Ross Callon, Stephane Litkowski, Bharath R, and Pushpasis Sarkarfor Ross Callon, Stephane Litkowski, Bharath R, and Pushpasis Sarkar for
their review of this document. their review of this document.
14. Informative References 14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
14.2. Informative References
[I-D.bryant-ipfrr-tunnels] [I-D.bryant-ipfrr-tunnels]
Bryant, S., Filsfils, C., Previdi, S., and M. Shand, "IP Bryant, S., Filsfils, C., Previdi, S., and M. Shand, "IP
Fast Reroute using tunnels", draft-bryant-ipfrr-tunnels-03 Fast Reroute using tunnels", draft-bryant-ipfrr-tunnels-03
(work in progress), November 2007. (work in progress), November 2007.
[I-D.filsfils-rtgwg-segment-routing] [I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", "Segment Routing Architecture", draft-filsfils-rtgwg-
draft-filsfils-rtgwg-segment-routing-01 (work in segment-routing-01 (work in progress), October 2013.
progress), October 2013.
[I-D.filsfils-rtgwg-segment-routing-use-cases]
Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
Crabbe, "Segment Routing Use Cases",
draft-filsfils-rtgwg-segment-routing-use-cases-02 (work in
progress), October 2013.
[I-D.gredler-rtgwg-igp-label-advertisement]
Gredler, H., Amante, S., Scholl, T., and L. Jalil,
"Advertising MPLS labels in IGPs",
draft-gredler-rtgwg-igp-label-advertisement-05 (work in
progress), May 2013.
[I-D.ietf-rtgwg-lfa-manageability] [I-D.ietf-rtgwg-lfa-manageability]
Litkowski, S., Decraene, B., Filsfils, C., Raza, K., Litkowski, S., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and p. psarkar@juniper.net, "Operational Horneffer, M., and p. psarkar@juniper.net, "Operational
management of Loop Free Alternates", management of Loop Free Alternates", draft-ietf-rtgwg-lfa-
draft-ietf-rtgwg-lfa-manageability-03 (work in progress), manageability-04 (work in progress), August 2014.
February 2014.
[I-D.psarkar-rtgwg-rlfa-node-protection] [I-D.psarkar-rtgwg-rlfa-node-protection]
psarkar@juniper.net, p., Gredler, H., Hegde, S., psarkar@juniper.net, p., Gredler, H., Hegde, S., Bowers,
Raghuveer, H., Bowers, C., and S. Litkowski, "Remote-LFA C., Litkowski, S., and H. Raghuveer, "Remote-LFA Node
Node Protection and Manageability", Protection and Manageability", draft-psarkar-rtgwg-rlfa-
draft-psarkar-rtgwg-rlfa-node-protection-04 (work in node-protection-05 (work in progress), June 2014.
progress), April 2014.
[ISOCORE2010] [ISOCORE2010]
So, N., Lin, T., and C. Chen, "LFA (Loop Free Alternates) So, N., Lin, T., and C. Chen, "LFA (Loop Free Alternates)
Case Studies in Verizon's LDP Network", 2010. Case Studies in Verizon's LDP Network", 2010.
[RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic [RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994. Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC1853] Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995. [RFC1853] Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001. Encoding", RFC 3032, January 2001.
[RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
June 2001.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An [RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002. December 2002.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007. Specification", RFC 5036, October 2007.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008. Engineering", RFC 5305, October 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008. for IPv6", RFC 5340, July 2008.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009. [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", [RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC
RFC 5714, January 2010. 5714, January 2010.
[RFC6571] Filsfils, C., Francois, P., Shand, M., Decraene, B., [RFC6571] Filsfils, C., Francois, P., Shand, M., Decraene, B.,
Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
Alternate (LFA) Applicability in Service Provider (SP) Alternate (LFA) Applicability in Service Provider (SP)
Networks", RFC 6571, June 2012. Networks", RFC 6571, June 2012.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
September 2013.
Authors' Addresses Authors' Addresses
Stewart Bryant Stewart Bryant
Cisco Systems Cisco Systems
250, Longwater, Green Park, 250, Longwater, Green Park,
Reading RG2 6GB, UK Reading RG2 6GB, UK
UK UK
Email: stbryant@cisco.com Email: stbryant@cisco.com
skipping to change at page 27, line 28 skipping to change at page 28, line 4
Email: stbryant@cisco.com Email: stbryant@cisco.com
Clarence Filsfils Clarence Filsfils
Cisco Systems Cisco Systems
De Kleetlaan 6a De Kleetlaan 6a
1831 Diegem 1831 Diegem
Belgium Belgium
Email: cfilsfil@cisco.com Email: cfilsfil@cisco.com
Stefano Previdi Stefano Previdi
Cisco Systems Cisco Systems
Email: sprevidi@cisco.com Email: sprevidi@cisco.com
URI:
Mike Shand Mike Shand
Independent Contributor Independent Contributor
Email: imc.shand@gmail.com Email: imc.shand@gmail.com
Ning So Ning So
Tata Communications Vinci Systems
Mobile Broadband Services
Email: Ning.So@tatacommunications.com Email: ning.so@vinci-systems.com
 End of changes. 60 change blocks. 
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