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rfc:rfc7916

Internet Engineering Task Force (IETF) S. Litkowski, Ed. Request for Comments: 7916 B. Decraene Category: Standards Track Orange ISSN: 2070-1721 C. Filsfils

                                                               K. Raza
                                                         Cisco Systems
                                                          M. Horneffer
                                                      Deutsche Telekom
                                                             P. Sarkar
                                                Individual Contributor
                                                             July 2016
           Operational Management of Loop-Free Alternates

Abstract

 Loop-Free Alternates (LFAs), as defined in RFC 5286, constitute an IP
 Fast Reroute (IP FRR) mechanism enabling traffic protection for IP
 traffic (and, by extension, MPLS LDP traffic).  Following early
 deployment experiences, this document provides operational feedback
 on LFAs, highlights some limitations, and proposes a set of
 refinements to address those limitations.  It also proposes required
 management specifications.
 This proposal is also applicable to remote-LFA solutions.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7916.

Litkowski, et al. Standards Track [Page 1] RFC 7916 LFA Manageability July 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://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.

Litkowski, et al. Standards Track [Page 2] RFC 7916 LFA Manageability July 2016

Table of Contents

 1. Introduction ....................................................4
    1.1. Requirements Language ......................................4
 2. Definitions .....................................................4
 3. Operational Issues with Default LFA Tiebreakers .................5
    3.1. Case 1: PE Router Protecting against Failures
         within Core Network ........................................5
    3.2. Case 2: PE Router Chosen to Protect against Core
         Failures while P Router LFA Exists .........................7
    3.3. Case 3: Suboptimal P Router Alternate Choice ...............8
    3.4. Case 4: No-Transit LFA Computing Node ......................9
 4. Need for Coverage Monitoring ....................................9
 5. Need for LFA Activation Granularity ............................10
 6. Configuration Requirements .....................................11
    6.1. LFA Enabling/Disabling Scope ..............................11
    6.2. Policy-Based LFA Selection ................................12
         6.2.1. Connected versus Remote Alternates .................12
         6.2.2. Mandatory Criteria .................................13
         6.2.3. Additional Criteria ................................14
         6.2.4. Evaluation of Criteria .............................14
         6.2.5. Retrieving Alternate Path Attributes ...............18
         6.2.6. ECMP LFAs ..........................................23
 7. Operational Aspects ............................................24
    7.1. No-Transit Condition on LFA Computing Node ................24
    7.2. Manual Triggering of FRR ..................................25
    7.3. Required Local Information ................................26
    7.4. Coverage Monitoring .......................................26
    7.5. LFAs and Network Planning .................................27
 8. Security Considerations ........................................28
 9. References .....................................................28
    9.1. Normative References ......................................28
    9.2. Informative References ....................................30
 Contributors ......................................................31
 Authors' Addresses ................................................31

Litkowski, et al. Standards Track [Page 3] RFC 7916 LFA Manageability July 2016

1. Introduction

 Following the first deployments of Loop-Free Alternates (LFAs), this
 document provides feedback to the community about the management
 of LFAs.
 o  Section 3 provides real use cases illustrating some limitations
    and suboptimal behavior.
 o  Section 4 provides requirements for LFA simulations.
 o  Section 5 proposes requirements for activation granularity and
    policy-based selection of the alternate.
 o  Section 6 expresses requirements for the operational management of
    LFAs and, in particular, a policy framework to manage alternates.
 o  Section 7 details some operational considerations of LFAs, such as
    IS-IS overload bit management and troubleshooting information.

1.1. 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].

2. Definitions

 o  Per-prefix LFA computation: Evaluation for the best alternate is
    done for each destination prefix, as opposed to the "per-next-hop"
    simplification technique proposed in Section 3.8 of [RFC5286].
 o  PE router: Provider Edge router.  These routers connect customers
    to each other.
 o  P router: Provider router.  These routers are core routers without
    customer connections.  They provide transit between PE routers,
    and they form the core network.
 o  Core network: subset of the network composed of P routers and
    links between them.
 o  Core link: network link part of the core network, i.e., a link
    between P routers.
 o  Link-protecting LFA: alternate providing protection against link
    failure.

Litkowski, et al. Standards Track [Page 4] RFC 7916 LFA Manageability July 2016

 o  Node-protecting LFA: alternate providing protection against node
    failure.
 o  Connected alternate: alternate adjacent (at the IGP level) to the
    Point of Local Repair (PLR) (i.e., an IGP neighbor).
 o  Remote alternate: alternate that does not share an IGP adjacency
    with the PLR.

3. Operational Issues with Default LFA Tiebreakers

 [RFC5286] introduces the notion of tiebreakers when selecting the LFA
 among multiple candidate alternate next hops.  When multiple LFAs
 exist, [RFC5286] has favored the selection of the LFA that provides
 the best coverage against the failure cases.  While this is indeed a
 goal, it is one among multiple goals, and in some deployments this
 leads to the selection of a suboptimal LFA.  The following sections
 detail real use cases related to such limitations.
 Note that the use case for LFA computation per destination
 (per-prefix LFA) is assumed throughout this analysis.  We also assume
 in the network figures that all IP prefixes are advertised with
 zero cost.

3.1. Case 1: PE Router Protecting against Failures within Core Network

       P1 --------- P2 ---------- P3 --------- P4
       |      1           100           1       |
       |                                        |
       | 100                                    | 100
       |                                        |
       |      1           100           1       |  1     5k
       P5 --------- P6 ---------- P7 --------- P8 --- P9 -- PE1
       | |         | |            |             |
     5k| |5k     5k| |5k          | 5k          | 5k
       | |         | |            |             |
       | +-- PE4 --+ |            +---- PE2 ----+
       |             |                   |
       +---- PE5 ----+                   | 5k
                                         |
                                        PE3
       Px routers are P routers using n * 10 Gbps links.
       PEs are connected using links with lower bandwidth.
                               Figure 1

Litkowski, et al. Standards Track [Page 5] RFC 7916 LFA Manageability July 2016

 In Figure 1, let us consider the traffic flowing from PE1 to PE4.
 The nominal path is P9-P8-P7-P6-PE4.  Let us now consider the failure
 of link P7-P8.  As the P4 primary path to PE4 is P8-P7-P6-PE4, P4 is
 not an LFA for P8 (because P4 will loop traffic back to P8), and the
 only available LFA is PE2.
 When the core link P8-P7 fails, P8 switches all traffic destined to
 PE4/PE5 towards the node PE2.  Hence, a PE node and PE links are used
 to protect against the failure of a core link.  Typically, PE links
 have less capacity than core links, and congestion may occur on PE2
 links.  Note that although PE2 is not directly affected by the
 failure, its links become congested, and its traffic will suffer from
 the congestion.
 In summary, in the case of P8-P7 link failure, the impact on customer
 traffic is:
 o  From PE2's point of view:
  • without LFA: no impact.
  • with LFA: traffic is partially dropped (but possibly

prioritized by a QoS mechanism). It must be highlighted that

       in such a situation, traffic not affected by the failure may be
       affected by the congestion.
 o  From P8's point of view:
  • without LFA: traffic is totally dropped until convergence

occurs.

  • with LFA: traffic is partially dropped (but possibly

prioritized by a QoS mechanism).

 Besides the congestion aspects of using a PE router as an alternate
 to protect against a core failure, a service provider may consider
 this to be a bad routing design and would want to prevent it.

Litkowski, et al. Standards Track [Page 6] RFC 7916 LFA Manageability July 2016

3.2. Case 2: PE Router Chosen to Protect against Core Failures while

    P Router LFA Exists
        P1 --------- P2 ------------ P3 ------- P4
        |      1           100       |     1    |
        |                            |          |
        | 100                        | 30       | 30
        |                            |          |
        |     1         50       50  |    10    |   1    5k
        P5 --------- P6 --- P10 ---- P7 ------- P8 --- P9 -- PE1
        | |         | |        \                |
      5k| |5k     5k| |5k       \ 5k            | 5k
        | |         | |          \              |
        | +-- PE4 --+ |           +---- PE2 ----+
        |             |                  |
        +---- PE5 ----+                  | 5k
                                         |
                                        PE3
           Px routers are P routers meshed with n * 10 Gbps links.
           PEs are meshed using links with lower bandwidth.
                               Figure 2
 In Figure 2, let us consider the traffic coming from PE1 to PE4.  The
 nominal path is P9-P8-P7-P10-P6-PE4.  Let us now consider the failure
 of the link P7-P8.  For P8, P4 is a link-protecting LFA and PE2 is a
 node-protecting LFA.  PE2 is chosen as the best LFA, due to the
 better type of protection that it provides.  Just as in case 1, this
 may lead to congestion on PE2 links upon LFA activation.

Litkowski, et al. Standards Track [Page 7] RFC 7916 LFA Manageability July 2016

3.3. Case 3: Suboptimal P Router Alternate Choice

                           +--- PE3 ---+
                          /             \
                    1000 /               \ 1000
                        /                 \
                +----- P1 ---------------- P2 ----+
                |      |        500        |      |
                | 10   |                   |      | 10
                |      |                   |      |
                R5     | 10                | 10   R7
                |      |                   |      |
                | 10   |                   |      | 10
                |      |        500        |      |
                +---- P3 ----------------- P4 ----+
                        \                 /
                    1000 \               / 1000
                          \             /
                           +--- PE1 ---+
                 Px routers are P routers.
                 P1-P2 and P3-P4 links are 1 Gbps links.
                 All other inter-Px links are 10 Gbps links.
                               Figure 3
 In Figure 3, let us consider the failure of link P1-P3.  For
 destination PE3, P3 has two possible alternates:
 o  P4, which is node-protecting
 o  R5, which is link-protecting
 P4 is chosen as the best LFA, due to the better type of protection
 that it provides.  However, for bandwidth capacity reasons, it
 may not be desirable to use P4.  A service provider may prefer to use
 high-bandwidth links as the preferred LFA.  In this example,
 preferring the shortest path over the type of protection may achieve
 the expected behavior, but in cases where metrics do not reflect the
 bandwidth, this technique would not work and some other criteria
 would need to be involved when selecting the best LFA.

Litkowski, et al. Standards Track [Page 8] RFC 7916 LFA Manageability July 2016

3.4. Case 4: No-Transit LFA Computing Node

                             P1       P2
                             |   \  /   |
                          50 | 50 \/ 50 | 50
                             |    /\    |
                             PE1-+  +-- PE2
                              \        /
                            45 \      / 45
                                -PE3-
                       (No-transit condition set)
                               Figure 4
 The IS-IS and OSPF protocols define some way to prevent a router from
 being used for transit.
 The IS-IS overload bit is defined in [ISO10589], and the OSPF R-bit
 is defined in [RFC5340].  Also, the OSPF stub router is defined in
 [RFC6987] as a method to prevent transit on a node by advertising
 MaxLinkMetric on all non-stub links.
 In Figure 4, PE3 has its no-transit condition set (permanently, for
 design reasons) and wants to protect traffic using an LFA for
 destination PE2.
 On PE3, the loop-free condition is not satisfied: 100 !< 45 + 45.
 PE1 is thus not considered as an LFA.  However, thanks to the
 no-transit condition on PE3, we know that PE1 will not loop the
 traffic back to PE3.  So, PE1 is an LFA to reach PE2.
 In the case of a no-transit condition set on a node, LFA behavior
 must be clarified.

4. Need for Coverage Monitoring

 As per [RFC6571], LFA coverage depends strongly on the network
 topology that is in use.  Even if the remote-LFA mechanism [RFC7490]
 significantly extends the coverage of the basic LFA specification,
 there are still some cases where protection would not be available.
 As network topologies are constantly evolving (network extension,
 additional capacity, latency optimization, etc.), the protection
 coverage may change.  Fast Reroute (FRR) functionality may be
 critical for some services supported by the network; a service
 provider must always know what type of protection coverage is
 currently available on the network.  Moreover, predicting protection
 coverage in the event of network topology changes is mandatory.

Litkowski, et al. Standards Track [Page 9] RFC 7916 LFA Manageability July 2016

 Today, network simulation tools associated with "what if" scenarios
 are often used by service providers for the overall network design
 (capacity, path optimization, etc.).  Sections 7.3, 7.4, and 7.5 of
 this document propose the addition of LFA information into such tools
 and within routers, so that a service provider may be able to:
 o  evaluate protection coverage after a topology change.
 o  adjust the topology change to cover the primary need (e.g.,
    latency optimization, bandwidth increase) as well as LFA
    protection.
 o  constantly monitor the LFA coverage in the live network and
    receive alerts.
 Documentation of LFA selection algorithms by implementers (default
 and tuning options) is important in order to make it possible for
 third-party modules to model these policy-based LFA selection
 algorithms.

5. Need for LFA Activation Granularity

 As in all FRR mechanisms, an LFA installs backup paths in the
 Forwarding Information Base (FIB).  Depending on the hardware used by
 a service provider, FIB resources may be critical.  Activating LFAs
 by default on all available components (IGP topologies, interfaces,
 address families, etc.) may lead to a waste of FIB resources, as
 generally only a few destinations in a network should be protected
 (e.g., loopback addresses supporting MPLS services) compared to the
 number of destinations in the Routing Information Base (RIB).
 Moreover, a service provider may implement multiple different FRR
 mechanisms in its networks for different applications (e.g.,
 Maximally Redundant Trees (MRTs), TE FRR).  In this scenario, an
 implementation MAY allow the computation of alternates for a specific
 destination even if the destination is already protected by another
 mechanism.  This will provide redundancy and permit the operator to
 select the best option for FRR, using a policy language.
 Section 6 provides some implementation guidelines.

Litkowski, et al. Standards Track [Page 10] RFC 7916 LFA Manageability July 2016

6. Configuration Requirements

 Controlling the selection of the best alternate and the granularity
 of LFA activation is a requirement for service providers.  This
 section defines configuration requirements for LFAs.

6.1. LFA Enabling/Disabling Scope

 The granularity of LFA activation SHOULD be controlled (as alternate
 next hops consume memory in the forwarding plane).
 An implementation of an LFA SHOULD allow its activation, with the
 following granularities:
 o  Per routing context: Virtual Routing and Forwarding (VRF),
    virtual/logical router, global routing table, etc.
 o  Per interface.
 o  Per protocol instance, topology, area.
 o  Per prefix: Prefix protection SHOULD have a higher priority
    compared to interface protection.  This means that if a specific
    prefix must be protected due to a configuration request, an LFA
    MUST be computed and installed for that prefix even if the primary
    outgoing interface is not configured for protection.
 An implementation of an LFA MAY allow its activation, with the
 following criteria:
 o  Per address family: IPv4 unicast, IPv6 unicast.
 o  Per MPLS control plane: For MPLS control planes that inherit
    routing decisions from the IGP routing protocol, the MPLS
    data plane may be protected by an LFA.  The implementation may
    allow an operator to control this inheritance of protection from
    the IP prefix to the MPLS label bound to this prefix.  The
    inheritance of protection will concern IP-to-MPLS, MPLS-to-MPLS,
    and MPLS-to-IP entries.  As an example, LDP and Segment Routing
    extensions [SEG-RTG-ARCH] for IS-IS and OSPF are control-plane
    eligible for this inheritance of protection.

Litkowski, et al. Standards Track [Page 11] RFC 7916 LFA Manageability July 2016

6.2. Policy-Based LFA Selection

 When multiple alternates exist, the LFA selection algorithm is based
 on tiebreakers.  Current tiebreakers do not provide sufficient
 control regarding how the best alternate is chosen.  This document
 proposes an enhanced tiebreaker allowing service providers to manage
 all specific cases:
 1.  An LFA implementation SHOULD support policy-based decisions for
     determining the best LFA.
 2.  Policy-based decisions SHOULD be based on multiple criteria, with
     each criterion having a level of preference.
 3.  If the defined policy does not allow the determination of a
     unique best LFA, an implementation SHOULD pick only one based on
     its own decision.  For load-balancing purposes, an implementation
     SHOULD also support the election of multiple LFAs.
 4.  The policy SHOULD be applicable to a protected interface or a
     specific set of destinations.  In the case of applicability to
     the protected interface, all destinations primarily routed on
     that interface SHOULD use the policy for that interface.
 5.  The choice of whether or not to dynamically re-evaluate policy
     (in the event of a policy change) is left to the implementation.
     If a dynamic approach is chosen, the implementation SHOULD
     recompute the best LFAs and reinstall them in the FIB without
     service disruption.  If a non-dynamic approach is chosen, the
     policy would be taken into account upon the next IGP event.  In
     this case, the implementation SHOULD support a command to
     manually force the recomputation/reinstallation of LFAs.

6.2.1. Connected versus Remote Alternates

 In addition to connected LFAs, tunnels (e.g., IP, LDP, RSVP-TE,
 Segment Routing) to distant routers may be used to complement LFA
 coverage (tunnel tail used as virtual neighbor).  When a router has
 multiple alternate candidates for a specific destination, it may have
 connected alternates and remote alternates (reachable via a tunnel).
 Connected alternates may not always provide an optimal routing path,
 and it may be preferable to select a remote alternate over a
 connected alternate.  Some uses of tunnels to extend LFA [RFC5286]
 coverage are described in [RFC7490] and [TI-LFA].  [RFC7490] and
 [TI-LFA] present some use cases for LDP tunnels and Segment Routing
 tunnels, respectively.  This document considers any type of tunneling
 techniques to reach remote alternates (IP, Generic Routing

Litkowski, et al. Standards Track [Page 12] RFC 7916 LFA Manageability July 2016

 Encapsulation (GRE), LDP, RSVP-TE, the Layer 2 Tunneling Protocol
 (L2TP), Segment Routing, etc.) and does not restrict the remote
 alternates to the uses presented in these other documents.
 In Figure 1, there is no P router alternate for P8 to reach PE4 or
 PE5, so P8 is using PE2 as an alternate; this may generate congestion
 when FRR is activated.  Instead, we could have a remote alternate for
 P8 to protect traffic to PE4 and PE5.  For example, a tunnel from P8
 to P3 (following the shortest path) can be set up, and P8 would be
 able to use P3 as a remote alternate to protect traffic to PE4 and
 PE5.  In this scenario, traffic will not use a PE link during FRR
 activation.
 When selecting the best alternate, the selection algorithm MUST
 consider all available alternates (connected or tunnel).  For
 example, with remote LFAs, computation of PQ sets [RFC7490] SHOULD be
 performed before the selection of the best alternate.

6.2.2. Mandatory Criteria

 An LFA implementation MUST support the following criteria:
 o  Non-candidate link: A link marked as "non-candidate" will never be
    used as an LFA.
 o  A primary next hop being protected by another primary next hop of
    the same prefix (ECMP case).
 o  Type of protection provided by the alternate: link protection or
    node protection.  In the case of preference for node protection,
    an implementation SHOULD support fallback to link protection if
    node protection is not available.
 o  Shortest path: lowest IGP metric used to reach the destination.
 o  Shared Risk Link Groups (SRLGs) (as defined in Section 3 of
    [RFC5286]; see also Section 6.2.4.1 for more details).

Litkowski, et al. Standards Track [Page 13] RFC 7916 LFA Manageability July 2016

6.2.3. Additional Criteria

 An LFA implementation SHOULD support the following criteria:
 o  A downstream alternate: Preference for a downstream path over a
    non-downstream path SHOULD be configurable.
 o  Link coloring with "include", "exclude", and preference-based
    systems (see Section 6.2.4.2).
 o  Link bandwidth (see Section 6.2.4.3).
 o  Alternate preference / node coloring (see Section 6.2.4.4).

6.2.4. Evaluation of Criteria

6.2.4.1. SRLGs

 Section 3 of [RFC5286] proposes the reuse of GMPLS IGP extensions to
 encode SRLGs [RFC5307] [RFC4203].  Section 3 of [RFC5286] also
 describes the algorithm to compute SRLG protection.
 When SRLG protection is computed, an implementation SHOULD allow the
 following:
 o  Exclusion of alternates in violation of SRLGs.
 o  Maintenance of a preference system between alternates based on
    SRLG violations.  How the preference system is implemented is out
    of scope for this document, but here are two examples:
  • Preference based on the number of violations. In this case,

more violations = less preferred.

  • Preference based on violation cost. In this case, each SRLG

violation has an associated cost. The lower violation costs

       are preferred.
 When applying SRLG criteria, the SRLG violation check SHOULD be
 performed on sources to alternates as well as alternates to
 destination paths, based on the SRLG set of the primary path.  In the
 case of remote LFAs, PQ-to-destination path attributes would be
 retrieved from the Shortest Path Tree (SPT) rooted at the PQ.

Litkowski, et al. Standards Track [Page 14] RFC 7916 LFA Manageability July 2016

6.2.4.2. Link Coloring

 Link coloring is a powerful system to control the choice of
 alternates.  Link colors are markers that will allow the encoding of
 properties of a particular link.  Protecting interfaces are tagged
 with colors.  Protected interfaces are configured to include some
 colors with a preference level and exclude others.
 Link color information SHOULD be signaled in the IGP, and
 administrative-group IGP extensions [RFC5305] [RFC3630] that are
 already standardized, implemented, and widely used SHOULD be used for
 encoding and signaling link colors.
                                  PE2
                                  |  +---- P4
                                  | /
                         PE1 ---- P1 --------- P2
                                  |     10 Gbps
                           1 Gbps |
                                  |
                                  P3
                               Figure 5
 In the example in Figure 5, the P1 router is connected to three P
 routers and two PEs.  P1 is configured to protect the P1-P4 link.  We
 assume that, given the topology, all neighbors are candidate LFAs.
 We would like to enforce a policy in the network where only a core
 router may protect against the failure of a core link and where
 high-capacity links are preferred.
 In this example, we can use the proposed link coloring by:
 o  Marking the PE links with the color RED.
 o  Marking the 10 Gbps core link with the color BLUE.
 o  Marking the 1 Gbps core link with the color YELLOW.
 o  Configuring the protected interface P1->P4 as follows:
  • Include BLUE, preference 200.
  • Include YELLOW, preference 100.
  • Exclude RED.

Litkowski, et al. Standards Track [Page 15] RFC 7916 LFA Manageability July 2016

 Using this, PE links will never be used to protect against P1-P4 link
 failure, and the 10 Gbps link will be preferred.
 The main advantage of this solution is that it can easily be
 duplicated on other interfaces and other nodes without change.  A
 service provider has only to define the color system (associate a
 color with a level of significance), as it is done already for TE
 affinities or BGP communities.
 An implementation of link coloring:
 o  SHOULD support multiple "include" and "exclude" colors on a single
    protected interface.
 o  SHOULD provide a level of preference between included colors.
 o  SHOULD support the configuration of multiple colors on a single
    protecting interface.

6.2.4.3. Bandwidth

 As mentioned in previous sections, not taking into account the
 bandwidth of an alternate could lead to congestion during FRR
 activation.  We propose that the bandwidth criteria be based on the
 link speed information, for the following reasons:
 o  If a router S has a set of X destinations primarily forwarded to
    N, using per-prefix LFAs may lead to having a subset of X
    protected by a neighbor N1, another subset by N2, another subset
    by Nx, etc.
 o  S is not aware of traffic flows to each destination, so in the
    case of FRR activation, S is not able to evaluate how much traffic
    will be sent to N1, N2, Nx, etc.
 Based on this, it is not useful to gather available bandwidth on
 alternate paths, as the router does not know how much bandwidth it
 requires for protection.  The proposed link speed approach provides a
 good approximation at low cost, as information is easily available.
 The bandwidth criteria of the policy framework SHOULD work in at
 least the following two ways:
 o  Prune: Exclude an LFA if the link speed to reach it is lower than
    the link speed of the primary next-hop interface.
 o  Prefer: Prefer an LFA based on its bandwidth to reach it compared
    to the link speed of the primary next-hop interface.

Litkowski, et al. Standards Track [Page 16] RFC 7916 LFA Manageability July 2016

6.2.4.4. Alternate Preference / Node Coloring

 Rather than tagging interfaces on each node (using link colors) to
 identify the types of alternate nodes (as an example), it would be
 helpful if routers could be identified in the IGP.  This would allow
 grouped processing on multiple nodes.  As an implementation needs to
 exclude some specific alternates (see Section 6.2.3), an
 implementation SHOULD be able to:
 o  give preference to a specific alternate.
 o  give preference to a group of alternates.
 o  exclude a specific alternate.
 o  exclude a group of alternates.
 A specific alternate may be identified by its interface, IP address,
 or router ID, and a group of alternates may be identified by a marker
 (tag) advertised in IGP.  The IGP encoding and signaling for marking
 groups of alternates SHOULD be done according to [RFC7917] and
 [RFC7777].  Using a tag/marker is referred to as "node coloring", as
 compared to the link coloring option presented in Section 6.2.4.2.
 Consider the following network:
                                PE3
                                |
                                |
                                PE2
                                |   +---- P4
                                |  /
                       PE1 ---- P1 -------- P2
                                |    10 Gbps
                         1 Gbps |
                                |
                                P3
                               Figure 6
 In the example above, each node is configured with a specific tag
 flooded through the IGP.
 o  PE1,PE3: 200 (non-candidate).
 o  PE2: 100 (edge/core).
 o  P1,P2,P3: 50 (core).

Litkowski, et al. Standards Track [Page 17] RFC 7916 LFA Manageability July 2016

 A simple policy could be configured on P1 to choose the best
 alternate for P1->P4 based on the function or role of the router,
 as follows:
 o  criterion 1 -> alternate preference: exclude tags 100 and 200.
 o  criterion 2 -> bandwidth.

6.2.5. Retrieving Alternate Path Attributes

6.2.5.1. Alternate Path

 The alternate path is composed of two distinct parts: PLR to
 alternate and alternate to destination.
                           N1 -- R1 ---- R2
                          /50     \       \
                         /         R3 --- R4
                        /                   \
                        S -------- E ------- D
                        \\                  //
                         \\                //
                          N2 ---- PQ ---- R5
                               Figure 7
 In Figure 7, we consider a primary path from S to D, with S using E
 as the primary next hop.  All metrics are 1, except that {S,N1} = 50.
 Two alternate paths are available:
 o  {S,N1,R1,R2|R3,R4,D}, where N1 is a connected alternate.  This
    consists of two sub-paths:
  • {S,N1}: path from the PLR to the alternate.
  • {N1,R1,R2|R3,R4,D}: path from the alternate to the destination.
 o  {S,N2,PQ,R5,D}, where the PQ is a remote alternate.  Again, the
    path consists of two sub-paths:
  • {S,N2,PQ}: path from the PLR to the alternate.
  • {PQ,R5,D}: path from the alternate to the destination.
 As displayed in Figure 7, some parts of the alternate path may fan
 out to multiple paths due to ECMP.

Litkowski, et al. Standards Track [Page 18] RFC 7916 LFA Manageability July 2016

6.2.5.2. Alternate Path Attributes

 Some criteria listed in the previous sections require the retrieval
 of some characteristics of the alternate path (SRLG, bandwidth,
 color, tag, etc.).  We call these characteristics "path attributes".
 A path attribute can record a list of node properties (e.g., node
 tag) or link properties (e.g., link color).
 This document defines two types of path attributes:
 o  Cumulative attribute: When a path attribute is cumulative, the
    implementation SHOULD record the value of the attribute on each
    element (link and node) along the alternate path.  SRLG, link
    color, and node color are cumulative attributes.
 o  Unitary attribute: When a path attribute is unitary, the
    implementation SHOULD record the value of the attribute only on
    the first element along the alternate path (first node, or first
    link).  Bandwidth is a unitary attribute.
                           N1 -- R1 ---- R2
                          /               \
                         / 50              R4
                        /                   \
                        S -------- E ------- D
                               Figure 8
 In Figure 8, N1 is a connected alternate to reach D from S.  We
 consider that all links have a RED color except {R1,R2}, which is
 BLUE.  We consider all links to be 10 Gbps except {N1,R1}, which is
 2.5 Gbps.  The bandwidth attribute collected for the alternate path
 will be 10 Gbps.  As the attribute is unitary, only the link speed of
 the first link {S,N1} is recorded.  The link color attribute
 collected for the alternate path will be {RED,RED,BLUE,RED,RED}.  As
 the attribute is cumulative, the value of the attribute on each link
 along the path is recorded.

6.2.5.3. Connected Alternate

 For an alternate path using a connected alternate:
 o  Attributes from the PLR to the alternate are retrieved from the
    interface connected to the alternate.  If the alternate is
    connected through multiple interfaces, the evaluation of
    attributes SHOULD be done once per interface (each interface is
    considered as a separate alternate) and once per ECMP group of
    interfaces (Layer 3 bundle).

Litkowski, et al. Standards Track [Page 19] RFC 7916 LFA Manageability July 2016

 o  Path attributes from the alternate to the destination are
    retrieved from the SPT rooted at the alternate.  As the alternate
    is a connected alternate, the SPT has already been computed to
    find the alternate, so there is no need for additional
    computation.
                           N1 -- R1 ---- R2
                        50//50             \
                         //                 \
                      i1//i2                 \
                       S -------- E -------- D
                               Figure 9
 In Figure 9, we consider a primary path from S to D, with S using E
 as the primary next hop.  All metrics are considered as 1 except
 {S,N1} links, which are using a metric of 50.  We consider the
 following SRLGs on links:
 o  {S,N1} using i1: SRLG1,SRLG10.
 o  {S,N1} using i2: SRLG2,SRLG20.
 o  {N1,R1}: SRLG3.
 o  {R1,R2}: SRLG4.
 o  {R2,D}: SRLG5.
 o  {S,E}: SRLG10.
 o  {E,D}: SRLG6.
 S is connected to the alternate using two interfaces: i1 and i2.
 If i1 and i2 are not part of an ECMP group, the evaluation of
 attributes is done once per interface, and each interface is
 considered as a separate alternate path.  Two alternate paths will be
 available with the associated SRLG attributes:
 o  Alternate path #1: {S,N1 using if1,R1,R2,D}:
    SRLG1,SRLG10,SRLG3,SRLG4,SRLG5.
 o  Alternate path #2: {S,N1 using if2,R1,R2,D}:
    SRLG2,SRLG20,SRLG3,SRLG4,SRLG5.
 Alternate path #1 is sharing risks with the primary path and may be
 pruned, or its preference may be revoked, per user-defined policy.

Litkowski, et al. Standards Track [Page 20] RFC 7916 LFA Manageability July 2016

 If i1 and i2 are part of an ECMP group, the evaluation of attributes
 is done once per ECMP group, and the implementation considers a
 single alternate path {S,N1 using if1|if2,R1,R2,D} with the following
 SRLG attributes: SRLG1,SRLG10,SRLG2,SRLG20,SRLG3,SRLG4,SRLG5.  The
 alternate path is sharing risks with the primary path and may be
 pruned, or its preference may be revoked, per user-defined policy.

6.2.5.4. Remote Alternate

 For alternate path using a remote alternate (tunnel):
 o  Attributes on the path from the PLR to the alternate are retrieved
    using the PLR's primary SPT (when using a PQ node from the
    P-space) or the immediate neighbor's SPT (when using a PQ from the
    extended P-space).  These are then combined with the attributes of
    the link(s) to reach the immediate neighbor.  In both cases, no
    additional SPT is required.
 o  Attributes from the remote alternate to the destination path may
    be retrieved from the SPT rooted at the remote alternate.  An
    additional forward SPT is required for each remote alternate
    (PQ node), as indicated in Section 2.3.2 of [REMOTE-LFA-NODE].  In
    some remote-alternate scenarios, like [TI-LFA], alternate-to-
    destination path attributes may be obtained using a different
    technique.
 The number of remote alternates may be very high.  In the case of
 remote LFAs, simulations of real-world network topologies have shown
 that as many as hundreds of PQs are possible.  The computational
 overhead of collecting all path attributes of all such PQs to
 destination paths could grow beyond reasonable levels.
 To handle this situation, implementations need to limit the number of
 remote alternates to be evaluated to a finite number before
 collecting alternate path attributes and running the policy
 evaluation.  Section 2.3.3 of [REMOTE-LFA-NODE] provides a way to
 reduce the number of PQs to be evaluated.
 Some other remote alternate techniques using static or dynamic
 tunnels may not require this pruning.

Litkowski, et al. Standards Track [Page 21] RFC 7916 LFA Manageability July 2016

                Link            Remote              Remote
                alternate       alternate           alternate
               -------------  ------------------   -------------
 Alternates    |  LFA      |  |   rLFA (PQs)   |   |  Static/  |
               |           |  |                |   |  Dynamic  |
 sources       |           |  |                |   |  tunnels  |
               -------------  ------------------   -------------
                    |                   |                  |
                    |                   |                  |
                    |        --------------------------    |
                    |        |  Prune some alternates |    |
                    |        | (sorting strategy)     |    |
                    |        --------------------------    |
                    |                   |                  |
                    |                   |                  |
                ------------------------------------------------
                |          Collect alternate attributes        |
                ------------------------------------------------
                                        |
                                        |
                             -------------------------
                             |    Evaluate policy    |
                             -------------------------
                                        |
                                        |
                                 Best alternates
                               Figure 10

6.2.5.5. Collecting Attributes in the Case of Multiple Paths

 As described in Section 6.2.5, there may be some situations where an
 alternate path or part of an alternate path fans out to multiple
 paths (e.g., ECMP).  When collecting path attributes in such a case,
 an implementation SHOULD consider the union of attributes of each
 sub-path.
 In Figure 7 (in Section 6.2.5.1), S has two alternate paths to
 reach D.  Each alternate path fans out to multiple paths due to ECMP.
 Consider the following link color attributes: all links are RED
 except {R1,R3}, which is BLUE.  The user wants to use an alternate
 path with only RED links.  The first alternate path
 {S,N1,R1,R2|R3,R4,D} does not fit the constraint, as {R1,R3} is BLUE.
 The second alternate path {S,N2,PQ,R5,D} fits the constraint and will
 be preferred, as it uses only RED links.

Litkowski, et al. Standards Track [Page 22] RFC 7916 LFA Manageability July 2016

6.2.6. ECMP LFAs

                                   10
                              PE2 - PE3
                               |     |
                            50 |  5  | 50
                               P1----P2
                               \\    //
                            50  \\  // 50
                                 PE1
               Links between P1 and PE1 are L1 and L2.
               Links between P2 and PE1 are L3 and L4.
                               Figure 11
 In Figure 11, the primary path from PE1 to PE2 is through P1, using
 ECMP on two parallel links -- L1 and L2.  In the case of standard
 ECMP behavior, if L1 is failing, the post-convergence next hop would
 become L2 and ECMP would no longer be in use.  If an LFA is
 activated, as stated in Section 3.4 of [RFC5286], "alternate
 next-hops may themselves also be primary next-hops, but need not be"
 and "alternate next-hops should maximize the coverage of the failure
 cases."  In this scenario, there is no alternate providing node
 protection, so PE1 will prefer L2 as the alternate to protect L1;
 this makes sense compared to post-convergence behavior.
 Consider a different scenario, again referring to Figure 11, where L1
 and L2 are configured as a Layer 3 bundle using a local feature and
 L3/L4 comprise a second Layer 3 bundle.  Layer 3 bundles are
 configured as if a link in the bundle is failing; the traffic must be
 rerouted out of the bundle.  Layer 3 bundles are generally introduced
 to increase bandwidth between nodes.  In a nominal situation, ECMP is
 still available from PE1 to PE2, but if L1 is failing, the
 post-convergence next hop would become the ECMP on L3 and L4.  In
 this case, LFA behavior SHOULD be adapted in order to reflect the
 bandwidth requirement.

Litkowski, et al. Standards Track [Page 23] RFC 7916 LFA Manageability July 2016

 We would expect the following FIB entry on PE1:
                 On PE1: PE2 +--> ECMP -> L1
                              |     |
                              |     +----> L2
                              |
                              +--> LFA (ECMP) -> L3
                                    |
                                    +----------> L4
                               Figure 12
 If L1 or L2 is failing, traffic must be switched on the LFA ECMP
 bundle rather than using the other primary next hop.
 As mentioned in Section 3.4 of [RFC5286], protecting a link within an
 ECMP by another primary next hop is not a MUST.  Moreover, as already
 discussed in this document, maximizing coverage against the failure
 cases may not be the right approach, and a policy-based choice of an
 alternate may be preferred.
 An implementation SHOULD allow setting a preference to protect a
 primary next hop with another primary next hop.  An implementation
 SHOULD also allow setting a preference to protect a primary next hop
 with a NON-primary next hop.  An implementation SHOULD allow the use
 of an ECMP bundle as an LFA.

7. Operational Aspects

7.1. No-Transit Condition on LFA Computing Node

 In Section 3.5 of [RFC5286], the setting of the no-transit condition
 (through the IS-IS overload bit or the OSPF R-bit) in an LFA
 computation is only taken into account for the case where a neighbor
 has the no-transit condition set.
 In addition to Inequality 1 (Loop-Free Criterion)
 (Distance_opt(N, D) < Distance_opt(N, S) + Distance_opt(S, D))
 [RFC5286], the IS-IS overload bit or the OSPF R-bit of the LFA
 calculating neighbor (S) SHOULD be taken into account.  Indeed, if it
 has the IS-IS overload bit set or the OSPF R-bit clear, no neighbor
 will loop traffic back to itself.
 An OSPF router acting as a stub router [RFC6987] SHOULD behave as if
 the R-bit was clear regarding the LFA computation.

Litkowski, et al. Standards Track [Page 24] RFC 7916 LFA Manageability July 2016

7.2. Manual Triggering of FRR

 Service providers often perform manual link shutdown (using a
 router's command-line interface (CLI)) to perform network
 changes/tests.  A manual link shutdown may be done at multiple
 levels: physical interface, logical interface, IGP interface,
 Bidirectional Forwarding Detection (BFD) session, etc.  In
 particular, testing or troubleshooting FRR requires that manual
 shutdown be performed on the remote end of the link, as a local
 shutdown would not generally trigger FRR.
 To permit such a situation, an implementation SHOULD support
 triggering/activating LFA FRR for a given link when a manual shutdown
 is done on a component that currently supports FRR activation.
 An implementation MAY also support FRR activation for a specific
 interface or a specific prefix on a primary next-hop interface and
 revert without any action on any running component of the node (links
 or protocols).  In this use case, the FRR activation time needs to be
 controlled by a timer in case the operator forgot to revert the
 traffic to the primary path.  When the timer expires, the traffic is
 automatically reverted to the primary path.  This will simplify the
 testing of the FRR path; traffic can then be reverted back to the
 primary path without causing a global network convergence.
 For example:
 o  If an implementation supports FRR activation upon a BFD
    session-down event, that implementation SHOULD support FRR
    activation when a manual shutdown is done on the BFD session.  But
    if an implementation does not support FRR activation upon a BFD
    session-down event, there is no need for that implementation to
    support FRR activation upon manual shutdown of a BFD session.
 o  If an implementation supports FRR activation upon a physical
    link-down event (e.g., Rx laser "off" detection, error threshold
    raised), that implementation SHOULD support FRR activation when a
    manual shutdown of a physical interface is done.  But if an
    implementation does not support FRR activation upon a physical
    link-down event, there is no need for that implementation to
    support FRR activation upon manual shutdown of a physical link.
 o  A CLI command may allow switching from the primary path to the FRR
    path to test the FRR path for a specific interface or prefix.
    There is no impact on the control plane; only the data plane of
    the local node may be changed.  A similar command may allow
    switching traffic back from the FRR path to the primary path.

Litkowski, et al. Standards Track [Page 25] RFC 7916 LFA Manageability July 2016

7.3. Required Local Information

 The introduction of LFAs in a network requires some enhancements to
 standard routing information provided by implementations.  Moreover,
 due to "non-100%" coverage, coverage information is also required.
 Hence, an implementation:
 o  MUST be able to display, for every prefix, the primary next hop as
    well as the alternate next-hop information.
 o  MUST provide coverage information per LFA activation domain (area,
    level, topology, instance, virtual router, address family, etc.).
 o  MUST provide the number of protected prefixes as well as
    non-protected prefixes globally.
 o  SHOULD provide the number of protected prefixes as well as
    non-protected prefixes per link.
 o  MAY provide the number of protected prefixes as well as
    non-protected prefixes per priority if the implementation supports
    prefix-priority insertion in the RIB/FIB.
 o  SHOULD provide a reason for choosing an alternate (policy and
    criteria) and for excluding an alternate.
 o  SHOULD provide the list of non-protected prefixes and the reason
    why they are not protected (e.g., no protection required, no
    alternate available).

7.4. Coverage Monitoring

 It is pretty easy to evaluate the coverage of a network in a nominal
 situation, but topology changes may change the level of coverage.  In
 some situations, the network may no longer be able to provide the
 required level of protection.  Hence, it becomes very important for
 service providers to receive alerts regarding changes in coverage.
 An implementation SHOULD:
 o  provide an alert system if total coverage (for a node) is below a
    defined threshold or when coverage returns to normal.
 o  provide an alert system if coverage for a specific link is below a
    defined threshold or when coverage returns to normal.

Litkowski, et al. Standards Track [Page 26] RFC 7916 LFA Manageability July 2016

 An implementation MAY:
 o  trigger an alert if a specific destination is not protected
    anymore or when protection comes back up for this destination.
 Although the procedures for providing alerts are beyond the scope of
 this document, we recommend that implementations consider standard
 and well-used mechanisms like syslog or SNMP traps.

7.5. LFAs and Network Planning

 The operator may choose to run simulations in order to ensure a
 certain type of full coverage for the whole network or a given subset
 of the network.  This is particularly likely if he operates the
 network in the sense of the third backbone profile described in
 Section 4 of [RFC6571]; that is, he seeks to design and engineer the
 network topology in such a way that a certain level of coverage is
 always achieved.  Obviously, a complete and exact simulation of the
 IP FRR coverage can only be achieved if the behavior is deterministic
 and the algorithm used is available to the simulation tool.  Thus, an
 implementation SHOULD:
 o  Behave deterministically in its LFA selection process.  That is,
    in the same topology and with the same policy configuration, the
    implementation MUST always choose the same alternate for a given
    prefix.
 o  Document its behavior.  The implementation SHOULD provide enough
    documentation regarding its behavior to allow an implementer of a
    simulation tool to foresee the exact choice of the LFA
    implementation for every prefix in a given topology.  This SHOULD
    take into account all possible policy configuration options.  One
    possible way to document this behavior is to disclose the
    algorithm used to choose alternates.

Litkowski, et al. Standards Track [Page 27] RFC 7916 LFA Manageability July 2016

8. Security Considerations

 The policy mechanism introduced in this document allows the tuning of
 the selection of the alternate.  This is not seen as a security
 threat, because:
 o  all candidates are already eligible as per [RFC5286] and
    considered usable.
 o  the policy is based on information from the router's own
    configuration and from the IGP, both of which are considered
    trusted.
 Hence, this document does not introduce any new security
 considerations as compared to [RFC5286].
 As noted above, the policy mechanism introduced in this document
 allows the tuning of the selection of the best alternate but does not
 change the list of alternates that are eligible.  As described in
 Section 7 of [RFC5286], this best alternate "can be used anyway when
 a different topological change occurs, and hence this can't be viewed
 as a new security threat."

9. References

9.1. Normative References

 [ISO10589] International Organization for Standardization,
            "Intermediate System to Intermediate System intra-domain
            routeing information exchange protocol for use in
            conjunction with the protocol for providing the
            connectionless-mode network service (ISO 8473)",
            ISO Standard 10589, 2002.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
            (TE) Extensions to OSPF Version 2", RFC 3630,
            DOI 10.17487/RFC3630, September 2003,
            <http://www.rfc-editor.org/info/rfc3630>.
 [RFC4203]  Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
            in Support of Generalized Multi-Protocol Label Switching
            (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
            <http://www.rfc-editor.org/info/rfc4203>.

Litkowski, et al. Standards Track [Page 28] RFC 7916 LFA Manageability July 2016

 [RFC5286]  Atlas, A., Ed., and A. Zinin, Ed., "Basic Specification
            for IP Fast Reroute: Loop-Free Alternates", RFC 5286,
            DOI 10.17487/RFC5286, September 2008,
            <http://www.rfc-editor.org/info/rfc5286>.
 [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
            Engineering", RFC 5305, DOI 10.17487/RFC5305,
            October 2008, <http://www.rfc-editor.org/info/rfc5305>.
 [RFC5307]  Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
            in Support of Generalized Multi-Protocol Label Switching
            (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
            <http://www.rfc-editor.org/info/rfc5307>.
 [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
            for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
            <http://www.rfc-editor.org/info/rfc5340>.
 [RFC6571]  Filsfils, C., Ed., Francois, P., Ed., Shand, M., Decraene,
            B., Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
            Alternate (LFA) Applicability in Service Provider (SP)
            Networks", RFC 6571, DOI 10.17487/RFC6571, June 2012,
            <http://www.rfc-editor.org/info/rfc6571>.
 [RFC6987]  Retana, A., Nguyen, L., Zinin, A., White, R., and D.
            McPherson, "OSPF Stub Router Advertisement", RFC 6987,
            DOI 10.17487/RFC6987, September 2013,
            <http://www.rfc-editor.org/info/rfc6987>.
 [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
            So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
            RFC 7490, DOI 10.17487/RFC7490, April 2015,
            <http://www.rfc-editor.org/info/rfc7490>.
 [RFC7777]  Hegde, S., Shakir, R., Smirnov, A., Li, Z., and B.
            Decraene, "Advertising Node Administrative Tags in OSPF",
            RFC 7777, DOI 10.17487/RFC7777, March 2016,
            <http://www.rfc-editor.org/info/rfc7777>.
 [RFC7917]  Sarkar, P., Ed., Gredler, H., Hegde, S., Litkowski, S.,
            and B. Decraene, "Advertising Node Administrative Tags in
            IS-IS", RFC 7917, DOI 10.17487/RFC7917, July 2016,
            <http://www.rfc-editor.org/info/rfc7917>.

Litkowski, et al. Standards Track [Page 29] RFC 7916 LFA Manageability July 2016

9.2. Informative References

 [REMOTE-LFA-NODE]
            Sarkar, P., Ed., Hegde, S., Bowers, C., Gredler, H., and
            S. Litkowski, "Remote-LFA Node Protection and
            Manageability", Work in Progress,
            draft-ietf-rtgwg-rlfa-node-protection-05, December 2015.
 [SEG-RTG-ARCH]
            Filsfils, C., Ed., Previdi, S., Ed., Decraene, B.,
            Litkowski, S., and R. Shakir, "Segment Routing
            Architecture", Work in Progress,
            draft-ietf-spring-segment-routing-09, July 2016.
 [TI-LFA]   Francois, P., Filsfils, C., Bashandy, A., Decraene, B.,
            and S. Litkowski, "Topology Independent Fast Reroute using
            Segment Routing", Work in Progress,
            draft-francois-segment-routing-ti-lfa-00, November 2013.

Litkowski, et al. Standards Track [Page 30] RFC 7916 LFA Manageability July 2016

Contributors

 Significant contributions were made by Pierre Francois, Hannes
 Gredler, Chris Bowers, Jeff Tantsura, Uma Chunduri, Acee Lindem, and
 Mustapha Aissaoui, whom the authors would like to acknowledge.

Authors' Addresses

 Stephane Litkowski (editor)
 Orange
 Email: stephane.litkowski@orange.com
 Bruno Decraene
 Orange
 Email: bruno.decraene@orange.com
 Clarence Filsfils
 Cisco Systems
 Email: cfilsfil@cisco.com
 Kamran Raza
 Cisco Systems
 Email: skraza@cisco.com
 Martin Horneffer
 Deutsche Telekom
 Email: Martin.Horneffer@telekom.de
 Pushpasis Sarkar
 Individual Contributor
 Email: pushpasis.ietf@gmail.com

Litkowski, et al. Standards Track [Page 31]

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