MPLS Egress Protection Framework
draft-shen-mpls-egress-protection-framework-06

Internet Engineering Task Force                               Yimin Shen
Internet-Draft                                           Minto Jeyananth
Intended status: Standards Track                        Juniper Networks
Expires: March 24, 2018                                   Bruno Decraene
                                                                  Orange
                                                          Hannes Gredler
                                                             RtBrick Inc
                                                          Carsten Michel
                                                        Deutsche Telekom
                                                             Huaimo Chen
                                                          Yuanlong Jiang
                                           Huawei Technologies Co., Ltd.
                                                      September 20, 2017


                    MPLS Egress Protection Framework
             draft-shen-mpls-egress-protection-framework-06

Abstract

   This document specifies a fast reroute framework for protecting IP/
   MPLS services and MPLS transport tunnels against egress node and
   egress link failures.  In this framework, the penultimate-hop router
   of an MPLS tunnel acts as the point of local repair (PLR) for egress
   node failure, and the egress router of the MPLS tunnel acts as the
   PLR for egress link failure.  Each of them pre-establishes a bypass
   tunnel to a protector.  Upon an egress node or link failure, the
   corresponding PLR performs local failure detection and local repair,
   by rerouting packets over the corresponding bypass tunnel.  The
   protector in turn performs context label switching or context IP
   forwarding to send the packets to the ultimate service
   destination(s).  This mechanism can be used to reduce traffic loss
   before global repair reacts to the failure and control plane
   protocols converge on the topology changes due to the failure.  The
   framework is applicable to all types of IP/MPLS services and MPLS
   tunnels.  Under the framework, service protocol extensions may be
   further specified to support service label distribution to the
   protector.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.



Yimin Shen, et al.       Expires March 24, 2018                 [Page 1]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 24, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   5
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Egress node protection  . . . . . . . . . . . . . . . . . . .   8
     5.1.  Reference topology  . . . . . . . . . . . . . . . . . . .   8
     5.2.  Egress node failure and detection . . . . . . . . . . . .   9
     5.3.  Protector and PLR . . . . . . . . . . . . . . . . . . . .  10
     5.4.  Protected egress  . . . . . . . . . . . . . . . . . . . .  11
     5.5.  Egress-protected tunnel . . . . . . . . . . . . . . . . .  11
     5.6.  Egress-protected service  . . . . . . . . . . . . . . . .  12
     5.7.  Egress-protected service to egress-protected tunnel
           mapping . . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.8.  Egress-protection bypass tunnel . . . . . . . . . . . . .  12
     5.9.  Context ID, context label, and context based forwarding .  12
     5.10. Advertisement and path resolution for context ID  . . . .  14
     5.11. Egress-protection bypass tunnel establishment . . . . . .  15
     5.12. Local Repair on PLR . . . . . . . . . . . . . . . . . . .  16
     5.13. Service label distribution from egress router to
           protector . . . . . . . . . . . . . . . . . . . . . . . .  17
     5.14. Centralized protector mode  . . . . . . . . . . . . . . .  17
   6.  Egress link protection  . . . . . . . . . . . . . . . . . . .  19
   7.  Global repair . . . . . . . . . . . . . . . . . . . . . . . .  22
   8.  Example: Layer-3 VPN egress protection  . . . . . . . . . . .  22



Yimin Shen, et al.       Expires March 24, 2018                 [Page 2]


Internet-Draft      MPLS Egress Protection Framework      September 2017


     8.1.  Egress node protection  . . . . . . . . . . . . . . . . .  24
     8.2.  Egress link protection  . . . . . . . . . . . . . . . . .  25
     8.3.  Global repair . . . . . . . . . . . . . . . . . . . . . .  25
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  25
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     12.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   In MPLS networks, LSPs (label switched paths) are widely used as
   transport tunnels to carry IP and MPLS services across MPLS domains.
   Examples of MPLS services are layer-2 VPNs, layer-3 VPNs,
   hierarchical LSPs, and others.  In general, a tunnel may carry
   multiple services of one or multiple types, given that the tunnel can
   satisfy both individual and aggregate requirements (e.g.  CoS, QoS)
   of these services.  The egress router of the tunnel should host the
   corresponding service instances of the services.  An MPLS service
   instance is responsible for forwarding service packets via an egress
   link to the service destination, based on a service label.  An IP
   service instance is responsible for forwarding service packets via an
   egress link to the service destination, based on the IP destination
   address.  The egress link is often called a PE-CE (provider edge -
   customer edge) link or attachment circuit (AC).

   Today, local repair based fast reroute mechanisms [RFC4090],
   [RFC5286], [RFC7490], [RFC7812] have been widely deployed to protect
   MPLS tunnels against transit link/node failures.  They can achieve
   fast restoration of traffic in the order of tens of milliseconds.
   Local repair refers to the scenario where the router upstream to an
   anticipated failure (aka.  PLR, i.e. point of local repair) pre-
   establishes a bypass tunnel to the router downstream of the failure
   (aka.  MP, i.e. merge point), and pre-installs the forwarding state
   of the bypass tunnel in the data plane.  The PLR also uses a rapid
   mechanism (e.g. link layer OAM, BFD, and others) to locally detect
   the failure in the data plane.  When the failure occurs, the PLR
   reroutes traffic through the bypass tunnel to the MP, allowing the
   traffic to continue to flow to the tunnel's egress router.

   This document describes a fast reroute framework for egress node and
   egress link protection.  Similar to transit link/node protection,
   this framework relies on a PLR to perform local failure detection and
   local repair.  In egress node protection, the PLR is the penultimate-
   hop router of a tunnel.  In egress link protection, the PLR is the
   egress router of the tunnel.  The framework relies on a so-called



Yimin Shen, et al.       Expires March 24, 2018                 [Page 3]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   "protector" to serve as the tailend of bypass tunnels.  The protector
   is a router that hosts some "protection service instances" and has
   its own connectivity or paths to service destinations.  When a PLR
   does local repair, the protector is responsible for performing
   "context label switching" for rerouted MPLS service packets and
   "context IP forwarding" for rerouted IP service packets.  Thus, the
   service packets can continue to reach service destinations with
   minimum disruption.

   This framework considers an egress node failure as a failure of a
   tunnel, as well as a failure of all the services carried by the
   tunnel, because service packets can no longer reach the service
   instances on the egress router.  Therefore, the framework addresses
   egress node protection at both tunnel level and service level
   simultaneously.  Likewise, the framework considers an egress link
   failure as a failure of all the services traversing the link, and
   addresses egress link protection at the service level.

   This framework requires that the destination (a CE or site) of a
   service MUST be dual-homed or have dual paths to an MPLS network,
   normally via two MPLS edge routers.  One of them is the egress router
   of the service's transport tunnel, and the other is a backup egress
   router.  In the "co-located" protector mode in this document, the
   backup egress router serves as a protector, and each service instance
   hosted on the router acts as a protection instance.  In the
   "centralized" protector mode (Section 5.14), a protector and a backup
   egress router may be decoupled, and each service instance on the
   backup egress router is simply considered as a "backup service
   instance".

   The framework is described by mainly referring to P2P (point-to-
   point) tunnels.  However, it is equally applicable to P2MP (point-to-
   multipoint), MP2P (multipoint-to-point) and MP2MP (multipoint-to-
   multipoint) tunnels, when a sub-LSP can be viewed as a P2P tunnel.

   The framework is a multi-service and multi-transport framework.  It
   assumes a generic model where each service is comprised of a common
   set of components, including service instance, service label, and
   service label distribution protocol, and transported over an MPLS
   tunnel.  Therefore, the framework is applicable to all existing and
   future types of MPLS tunnels and IP/MPLS services.

   The framework does not require extensions for the existing signaling
   and label distribution protocols (e.g.  RSVP, LDP, BGP, etc.) of MPLS
   tunnels, because transport tunnels and bypass tunnels are expected to
   be established by using the generic mechanisms provided by the
   protocols.  However, the framework does not preclude future
   extensions to the protocols which may facilitate the procedures.  One



Yimin Shen, et al.       Expires March 24, 2018                 [Page 4]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   example of such extension is [RSVP-EP].  The framework may need
   extensions for IGPs and service label distribution protocols, to
   support protection establishment and context label switching.  This
   document provides guidelines for these extensions, but the specific
   details SHOULD be addressed in separate documents.

   The framework is intended to complement control-plane convergence and
   global repair, which are traditionally used to recover networks from
   egress node and egress link failures.  Control-plane convergence
   relies on control protocols to react on the topology changes due to a
   failure.  Global repair relies an ingress router to remotely detect a
   failure and switch traffic to an alternative path.  An example of
   global repair is the BGP Prefix Independent Convergence mechanism
   [BGP-PIC] for BGP established services.  Compared with these
   mechanisms, this framework is considered as faster in traffic
   restoration, due to the nature of local failure detection and local
   repair.  However, it is RECOMMENDED that the framework SHOULD be used
   in conjunction with control-plane convergence or global repair, in
   order to take the advantages of both approaches to achieve more
   effective protection.  That is, the framework provides fast and
   temporary repair, and control-plane convergence or global repair
   provides ultimate and permanent repair.

2.  Specification of Requirements

   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.

3.  Terminology

   Egress router - A router at the egress endpoint of a tunnel.  It
   hosts service instances for all the services carried by the tunnel,
   and has connectivity with the destinations of the services.

   Egress node failure - A failure of an egress router.

   Egress link failure - A failure of the egress link (e.g.  PE-CE link,
   attachment circuit) of a service.

   Egress failure - An egress node failure or an egress link failure.

   Egress-protected tunnel - A tunnel whose egress router is protected
   by a mechanism according to this framework.  The egress router is
   hence called a protected egress router.






Yimin Shen, et al.       Expires March 24, 2018                 [Page 5]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   Egress-protected service - An IP or MPLS service which is carried by
   an egress-protected tunnel, and hence protected by a mechanism
   according to this framework.

   Backup egress router - Given an egress-protected tunnel and its
   egress router, this is another router which has connectivity with all
   or a subset of the destinations of the egress-protected services
   carried by the egress-protected tunnel.  The service instances on
   this router are called backup service instances, and the
   corresponding services are called backup services.

   Backup service instance - A service instance which is hosted by a
   backup egress router, and corresponding to an egress-protected
   service on a protected egress router.

   Protector - A role acted by a router as an alternate of a protected
   egress router, to handle service packets in the event of an egress
   failure.  It protects an egress-protected tunnel, and hosts
   protection service instances for the egress-protected services
   carried by the tunnel.  A protector may or may not be physically co-
   located with or decoupled from a backup egress router, depending on
   the co-located or centralized protector mode.

   Protection service instance - A service instance hosted by a
   protector, protecting the service instance of an egress-protected
   service on a protected egress router.  A protection service instance
   is a backup service instance, if the protector is co-located with a
   backup egress router.

   PLR - A router at the point of local repair.  In egress node
   protection, it is the penultimate-hop router on an egress-protected
   tunnel.  In egress link protection, it is the egress router of the
   egress-protected tunnel.

   Protected egress {E, P} - A virtual node consisting of an ordered
   pair of egress router E and protector P.  It serves as the virtual
   destination for an egress-protected tunnel.  It also serves as the
   virtual location of service instances for the egress-protected
   services carried by the tunnel.

   Context identifier (ID) - A globally unique IP address assigned to a
   protected egress {E, P}.

   Context label - A non-reserved label assigned to a context ID by a
   protector.

   Egress-protection bypass tunnel - A tunnel used for rerouting service
   packets around an egress failure.  In egress node protection, it is



Yimin Shen, et al.       Expires March 24, 2018                 [Page 6]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   established from a penultimate-hop router (i.e.  PLR) to a protector,
   bypassing a protected egress router.  In egress link protection, it
   is established from a protected egress router (i.e.  PLR) to a
   protector, bypassing an egress link.

   Co-located protector mode - The scenario where a protector and a
   backup egress router are co-located as one router, and hence each
   backup service instance serves as a protection service instance.

   Centralized protector mode - The scenario where a protector is a
   dedicated router, and is decoupled from backup egress routers.

   Context label switching - Label switching performed by a protector,
   in the label space of an egress router indicated by a context label.

   Context IP forwarding - IP forwarding performed by a protector, in
   the IP address space of an egress router indicated by a context
   label.

4.  Requirements

   This document considers the followings as the design requirements of
   this egress protection framework.

   o  The framework must support P2P tunnels.  It should equally support
      P2MP, MP2P and MP2MP tunnels, by treating each sub-LSP as a P2P
      tunnel.

   o  The framework must support multi-service and multi-transport
      networks.  It must accommodate existing and future signaling and
      label-distribution protocols of tunnels and bypass tunnels,
      including RSPV, LDP, BGP, IGP, segment routing, and others.  It
      must also accommodate existing and future IP/MPLS services,
      including layer-2 VPNs, layer-3 VPNs, hierarchical LSP, and
      others.  It must provide a generic solution for environments where
      different types of services and tunnels may co-exist.

   o  The framework must consider minimizing disruption for deployment.
      It should only involve routers close to egress, and be transparent
      to ingress routers and other transit routers.

   o  In egress node protection, for scalability and performance
      reasons, a PLR must be agnostic to services and service labels,
      like PLRs in transit link/node protection.  It must maintain
      bypass tunnels and bypass forwarding state on a per-transport-
      tunnel basis, rather than per-service-destination or per-service-
      label basis.  It should also support bypass tunnel sharing between
      transport tunnels.



Yimin Shen, et al.       Expires March 24, 2018                 [Page 7]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   o  A PLR must be able to use its local visibility or information of
      routing and/or TE topology to compute or resolve a path for a
      bypass tunnel to a protector.

   o  A protector must be able to perform context label switching for
      rerouted MPLS service packets, based on service label(s) assigned
      by an egress router.  It must be able to perform context IP
      forwarding for rerouted IP service packets, in the public or
      private IP address space used by an egress router.

   o  The framework must be able to work seamlessly with transit link/
      node protection mechanisms to achieve end-to-end coverage.

   o  The framework must be able to work in conjunction with global
      repair and control plane convergence.

5.  Egress node protection

5.1.  Reference topology

   This document refers to the following topology when describing the
   procedures for egress node protection.





























Yimin Shen, et al.       Expires March 24, 2018                 [Page 8]


Internet-Draft      MPLS Egress Protection Framework      September 2017


                  services 1, ..., N
        =====================================> tunnel

      I ------ R1 ------- PLR --------------- E ----
   ingress          penultimate-hop        egress    \
                           |  .           (primary    \
                           |  .            service     \
                           |  .            instances)   \
                           |  .                          \
                           |  .                           \   service
                           |  .                             destinations
                           |  .                           / (CEs, sites)
                           |  .                          /
                           |  . bypass                  /
                           |  . tunnel                 /
                           |  .                       /
                           |  ...............        /
                           R2 --------------- P ----
                                          protector
                                         (protection
                                          service
                                          instances)


                                 Figure 1

5.2.  Egress node failure and detection

   An egress node failure refers to the failure of an MPLS tunnel's
   egress router.  At the service level, it also means a service
   instance failure for each IP/MPLS service carried by the tunnel.

   Ideally, an egress node failure can be detected by an adjacent router
   (i.e.  PLR in this framework) using a node liveness detection
   mechanism, or based on a collective failure of all the links to that
   node.  However, the assumption is that the mechanisms SHOULD be
   reasonably fast, i.e. faster than control plane failure detection and
   remote failure detection.  Otherwise, local repair will not be able
   to provide much gain in restoring traffic compared to control plane
   convergence or global repair.  In general, the speed, accuracy, and
   reliability of a mechanism are the key factors to decide its
   applicability in egress node protection.  This document provides the
   following guidelines in this regard.

   o  If the PLR has a reasonably fast mechanism to detect and
      differentiate a link failure and an egress node failure, it SHOULD
      set up both link protection and egress node protection, and
      trigger one and only one protection upon a corresponding failure.



Yimin Shen, et al.       Expires March 24, 2018                 [Page 9]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   o  If the PLR has a fast mechanism to detect a link failure and an
      egress node failure, but cannot distinguish them; Or, if the PLR
      has a fast mechanism to detect a link failure only, but not an
      egress node failure, the PLR has two options:

      1.  It MAY set up link protection only, and leave the egress node
          failure to global repair and control plane convergence to
          handle.

      2.  It MAY set up egress node protection only, and treat a link
          failure as a trigger for the egress node protection.  However,
          the assumption is that treating a link failure as an egress
          node failure MUST NOT have a negative impact on services.
          Otherwise, it SHOULD adopt the previous option.

5.3.  Protector and PLR

   A router is assigned to the "protector" role to protect a tunnel and
   the services carried by the tunnel against an egress node failure.
   The protector is responsible for hosting a protection service
   instance for each protected service, serving as the tailend of a
   bypass tunnel, and performing context label switching and/or context
   IP forwarding for rerouted service packets.

   A tunnel can be protected by only one protector at a given time.
   Multiple tunnels to a given egress router may be protected by a
   common protector or different protectors.  A protector may protect
   multiple tunnels with a common egress router or different egress
   routers.

   For each tunnel, its penultimate-hop router acts as a PLR.  The PLR
   pre-establishes a bypass tunnel to the protector, and pre-installs
   bypass forwarding state in the data plane.  Upon detection of an
   egress node failure, the PLR reroutes all the service packets
   received on the tunnel though the bypass tunnel to the protector.
   For MPLS service packets, the PLR keeps service labels intact in the
   packets.  The protector in turn forwards the rerouted service packets
   towards the ultimate service destinations.  Specifically, it performs
   context label switching for MPLS service packets, based on service
   labels assigned by the protected egress router; It performs context
   IP forwarding for IP service packets, based on their destination
   addresses.

   The protector MUST have its own connectivity with each service
   destination, via a direct link or a multi-hop path, which MUST NOT
   traverse the protected egress router or be affected by the egress
   node failure.  This also requires that each service destination MUST
   be dual-homed or have dual paths to the egress router and a backup



Yimin Shen, et al.       Expires March 24, 2018                [Page 10]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   egress router which serves as the protector.  Each protection service
   instance on the protector relies on such connectivity to set up
   forwarding state for context label switching and/or context IP
   forwarding.

5.4.  Protected egress

   This document introduces the notion of "protected egress" as a
   virtual node consisting of the egress router E of a tunnel and a
   protector P.  It is denoted by an ordered pair of {E, P}, indicating
   the primary-and-protector relationship between the two routers.  It
   serves as the virtual destination of the tunnel, and the virtual
   location of service instances for the services carried by the tunnel.
   The tunnel and services are considered as being "associated" with the
   protected egress {E, P}.

   A given egress router E may be the tailend of multiple tunnels.  In
   general, the tunnels may be protected by multiple protectors, e.g.
   P1, P2, and so on, with each Pi protecting a subset of the tunnels.
   Thus, these routers form multiple protected egresses, i.e. {E, P1} ,
   {E, P2}, and so on.  Each tunnel is associated with one and only one
   protected egress {E, Pi}. All the services carried by the tunnel are
   then automatically associated with the same protected egress {E, Pi}.
   Conversely, a service associated with a protected egress {E, Pi} MUST
   be carried by a tunnel associated with the same protected egress {E,
   Pi}. This mapping MUST be ensured by the ingress router of the tunnel
   and the service (Section 5.7).

   Two routers X and Y may be protectors for each other.  In this case,
   they form two distinct protected egresses {X, Y} and {Y, X}.

5.5.  Egress-protected tunnel

   A tunnel, which is associated with a protected egress {E, P}, is
   called an egress-protected tunnel.  It is associated with one and
   only one protected egress {E, P}. Multiple egress-protected tunnels
   may be associated with a given protected egress {E, P}. In this case,
   they share the common egress router and protector, but may or may not
   share a common ingress router, a common path, or a common PLR.

   An egress-protected tunnel is considered as logically "destined" for
   its protected egress {E, P}. However, its path MUST be resolved and
   established with E as the physical tailend.








Yimin Shen, et al.       Expires March 24, 2018                [Page 11]


Internet-Draft      MPLS Egress Protection Framework      September 2017


5.6.  Egress-protected service

   A service, which is associated with a protected egress {E, P}, is
   called an egress-protected service.  The egress router E hosts the
   primary instance of the service, and the protector P hosts the
   protection instance.

   An egress-protected service is associated with one and only one
   protected egress {E, P}. Multiple egress-protected services may be
   associated with a given protected egress {E, P}. In this case, these
   services share the common egress router and protector, but may or may
   not share a common egress-protected tunnel or a common ingress
   router.

5.7.  Egress-protected service to egress-protected tunnel mapping

   An egress-protected service MUST be mapped to an egress-protected
   tunnel by its ingress router, based on the common protected egress
   {E, P} of the service and the tunnel.  This is achieved by
   introducing the notion of "context ID" for protected egress {E, P},
   as described in (Section 5.9).

5.8.  Egress-protection bypass tunnel

   An egress-protected tunnel destined for a protected egress {E, P}
   MUST have a bypass tunnel from its PLR to the protector P.  This
   bypass tunnel is called an egress-protection bypass tunnel.  The
   bypass tunnel is considered as logically "destined" for the protected
   egress {E, P}. However, due to its bypass tunnel nature, it MUST be
   resolved and established with P as the physical tailend and E as the
   node to avoid.  The bypass tunnel MUST have the property that it MUST
   NOT be affected by any topology change caused by an egress node
   failure.

   An egress-protection bypass tunnel is associated with one and only
   one protected egress {E, P}. A PLR may share an egress-protection
   bypass tunnel between multiple egress-protected tunnels associated
   with a common protected egress {E, P}. For multiple egress-protected
   tunnels associated with a common protected egress {E, P}, there may
   be one or multiple egress-protection bypass tunnels from one or
   multiple PLRs to the protector P, depending on the paths of the
   egress-protected tunnels.

5.9.  Context ID, context label, and context based forwarding

   In this framework, a globally unique IPv4/v6 address is assigned to a
   protected egress {E, P} to serve as the identifier of the protected
   egress {E, P}. It is called a "context ID" due to its specific usage



Yimin Shen, et al.       Expires March 24, 2018                [Page 12]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   in context label switching and context IP forwarding on the
   protector.  It is an IP address that is logically owned by both the
   egress router and the protector.  For the egress node, it indicates
   the protector.  For the protector, it indicates the egress router,
   particularly the egress router's forwarding context.  For other
   routers in the network, it is an address reachable via both the
   egress router and the protector in the routing domain and the TE
   domain (Section 5.10).

   The main purpose of a context ID is to coordinate ingress router,
   egress router, PLR and protector in setting up egress protection.
   Given an egress-protected service associated with a protected egress
   {E, P}, its context ID is used as below:

   o  If the service is an MPLS service, when E distributes a service
      label binding message to the ingress router, E attaches the
      context ID to the message.  If the service is an IP service, when
      E advertises the service destination address to the ingress
      router, E also attaches the context ID to the advertisement
      message.  How the context ID is encoded in the messages is a
      choice of the service protocol, and may need protocol extensions
      to define a dedicated "context ID" object.

   o  The ingress router uses the context ID as destination to establish
      or resolve an egress-protected tunnel.  The ingress router then
      maps the service to the tunnel for transportation.  In this
      process, the special semantics of the context ID is transparent to
      the ingress router.  The ingress router only views the context ID
      as an IP address of E, and behaves in the same manner as in
      establishing or resolving a regular transport tunnel, although the
      end result is an egress-protected tunnel.

   o  The context ID is conveyed to the PLR by the signaling protocol of
      the egress-protected tunnel, or learned by the PLR via an IGP or
      topology-driven label distribution protocol.  The PLR uses the
      context ID as destination to establish or resolve an egress-
      protection bypass tunnel to P while avoiding E.

   o  P maintains a dedicated label space or a dedicated IP address
      space for E, depending on whether the service is MPLS or IP.  This
      is referred to as "E's label space" or "E's IP address space",
      respectively.  P uses the context ID to identify the space.

   o  If the service is an MPLS service, E also distributes the service
      label binding message to P.  This is the same label binding
      message that E advertises to the ingress router, attached with the
      context ID.  Based on the context ID, P installs the service label
      in an MPLS forwarding table corresponding to E's label space.  If



Yimin Shen, et al.       Expires March 24, 2018                [Page 13]


Internet-Draft      MPLS Egress Protection Framework      September 2017


      the service is an IP service, P installs an IP route in an IP
      forwarding table corresponding to E's IP address space.  In either
      case, the protection service instance on P interprets the service
      and constructs forwarding state for the route based on P's own
      connectivity to the service's destination.

   o  P assigns a non-reserved label to the context ID.  In the data
      plane, this label represents the context ID and indicates E's
      label space and IP address space.  Therefore, it is called a
      "context label".

   o  The PLR may establish the egress-protection bypass tunnel to P in
      several manners.  If the bypass tunnel is established by RSVP, the
      PLR signals the bypass tunnel with the context ID as destination,
      and P binds the context label to the bypass tunnel.  If the bypass
      tunnel is established by LDP, P advertises the context label for
      the context ID as an IP prefix FEC.  If the bypass tunnel is
      established by the PLR in a hierarchical manner, the PLR treats
      the context label as a one-hop LSP over a regular bypass tunnel to
      P (e.g. a bypass tunnel to P's loopback IP address).  If the
      bypass tunnel is constructed by using segment routing, the bypass
      tunnel is represented by a stack of SID labels with the context
      label as the inner-most SID label (Section 5.11).  In any case,
      the bypass tunnel is a UHP tunnel whose incoming label at P is the
      context label.

   o  During local repair, all the service packets received by P on the
      bypass tunnel will have the context label as top label.  P will
      first pop the context label.  For an MPLS service packet, P will
      further look up the service label in E's label space indicated by
      the context label, which is called context label switching.  For
      an IP service packet, P will look up the IP destination address in
      E's IP address space indicated by the context label, which is
      called context IP forwarding.

5.10.  Advertisement and path resolution for context ID

   Path resolution or computation for a context ID is done on ingress
   routers for egress-protected tunnels, and on PLRs for egress-
   protection bypass tunnels.  Therefore, given a protected egress {E,
   P} and its context ID, E and P MUST coordinate the context ID in the
   routing domain and the TE domain via IGP advertisement.  The context
   ID MUST be advertised in such a manner that any egress-protected
   tunnels MUST have E as tailend, and any egress-protection bypass
   tunnels MUST have P as tailend while avoiding E.

   This document suggests two approaches:




Yimin Shen, et al.       Expires March 24, 2018                [Page 14]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   1.  The first approach is called "proxy mode".  It requires E and P,
       but not the PLR, to have the knowledge of the egress protection
       schema.  E and P advertise the context ID as a virtual proxy node
       (i.e. a logical node) connected to the two routers, with the link
       between the proxy node and E having more preferable IGP and TE
       metrics than the link between the proxy node and P.  Therefore,
       all egress-protected tunnels destined for the context ID should
       automatically follow the shortest IGP or TE paths to E.  Each PLR
       will no longer view itself as a penultimate-hop, but rather two
       hops away from the proxy node, via E.  The PLR will be able to
       find a bypass path via P to the proxy node, while the bypass
       tunnel should actually be terminated by P.

   2.  The second approach is called "alias mode".  It requires P and
       the PLR, but not E, to have the knowledge of the egress
       protection schema.  E simply advertises the context ID as a
       regular IP address.  P advertises the context ID and the context
       label by using a "context ID label binding" advertisement.  The
       advertisement MUST be understood by the PLR.  In both routing
       domain and TE domain, the context ID is only reachable via E.
       This ensures that all egress-protected tunnels destined for the
       context ID should have E as tailend.  Based on the "context ID
       label binding" advertisement, the PLR can establish an egress-
       protection bypass tunnel in several manners (Section 5.11).  The
       "context ID label binding" advertisement is defined as IGP
       mirroring context segment in [SR-ARCH], [SR-OSPF] and [SR-ISIS].
       These IGP extensions are generic in nature, and have broad
       applicability beyond segment routing.

   In a scenario where an egress-protected tunnel is an inter-area or
   inter-AS tunnel, its associated context ID MUST be propagated from
   the residing area/AS to the other areas/AS' via IGP or BGP, so that
   the ingress router of the tunnel can obtain the reachability to the
   context ID.  The propagation process of the context ID SHOULD be the
   same as that of a regular IP address in an inter-area/AS environment.

5.11.  Egress-protection bypass tunnel establishment

   A PLR MUST know the context ID of a protected egress {E, P} in order
   to establish an egress-protection bypass tunnel.  The information is
   obtained from the signaling or label distribution protocol of the
   egress-protected tunnel.  The PLR may or may not need to have the
   knowledge of the egress protection schema.  All it does is to set up
   a bypass tunnel to a context ID while avoiding the next-hop router
   (i.e. egress router).  This is achievable by using a constraint-based
   computation algorithm similar to those which are commonly used to
   compute traffic engineering paths and loop-free alternate (LFA)
   paths.  Since the context ID is advertised in the routing domain and



Yimin Shen, et al.       Expires March 24, 2018                [Page 15]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   the TE domain by IGP according to Section 5.10, the PLR should be
   able to resolve or establish such a bypass path with the protector as
   tailend.  In some cases like the proxy mode, the PLR may do so in the
   same manner as transit node protection.

   An egress-protection bypass tunnel may be established via several
   methods:

   (1) It may be established by a signaling protocol (e.g.  RSVP), with
   the context ID as destination.  The protector binds the context label
   to the bypass tunnel.

   (2) It may be formed by a topology driven protocol (e.g.  LDP with
   various LFA mechanisms).  The protector advertises the context ID as
   an IP prefix FEC, and binds the context label to it.

   (3) It may be constructed as a hierarchical tunnel.  When the
   protector uses the alias mode (Section 5.10), the PLR will have the
   knowledge of the context ID, context label, and protector (i.e. the
   advertiser).  The PLR can then establish the bypass tunnel in a
   hierarchical manner, with the context label as a one-hop LSP over a
   regular bypass tunnel to the protector's IP address (e.g. loopback
   address).  This regular bypass tunnel may be established by RSVP,
   LDP, segment routing, and others.

5.12.  Local Repair on PLR

   In this framework, a PLR is agnostic to services and service labels.
   This obviates the need to maintain bypass forwarding state on a per-
   service basis, and allows bypass tunnel sharing between egress-
   protected tunnels.  During local repair, the PLR simply reroutes all
   service packets received on a tunnel to the corresponding bypass
   tunnel.  Service labels remain intact in MPLS service packets.

   Label operation during the rerouting depends on the bypass tunnel's
   characteristics.  If the bypass tunnel is a single level tunnel, the
   rerouting will involve swapping the incoming label of the egress-
   protected tunnel to the outgoing label of the bypass tunnel.  If the
   bypass tunnel is a hierarchical tunnel, the rerouting will involve
   swapping the incoming label of the egress-protected tunnel to a
   context label, and pushing the outgoing label of a regular bypass
   tunnel.  If the bypass tunnel is constructed by segment routing, the
   rerouting will involve swapping the incoming label of the egress-
   protected tunnel to a stack of SID labels, with a context label as
   the inner-most SID label.






Yimin Shen, et al.       Expires March 24, 2018                [Page 16]


Internet-Draft      MPLS Egress Protection Framework      September 2017


5.13.  Service label distribution from egress router to protector

   As mentioned in previous sections, when a protector receives a
   rerouted MPLS service packet, it performs context label switching
   based on the packet's service label which is assigned by the
   corresponding egress router.  In order to achieve this, the protector
   MUST maintain such kind of service labels in dedicated label spaces
   on a per protected egress {E, P} basis, i.e. one label space for each
   egress router that it protects.

   Also, there MUST be a service label distribution protocol session
   between each egress router and the protector.  Through this protocol,
   the protector learns the label binding of each egress-protected
   service.  This is the same label binding that the egress router
   advertises to the corresponding ingress router, attached with a
   context ID.  The corresponding protection service instance on the
   protector recognizes the service, and resolves forwarding state based
   on its own connectivity with the service's destination.  It then
   installs the service label with the forwarding state in the label
   space of the egress router, which is indicated by the context ID
   (i.e. context label).

   Different service protocols may use different mechanisms for such
   kind of label distribution.  Specific protocol extensions may be
   needed on a per-protocol basis or per-service-type basis.  The
   specific details of the extensions SHOULD be specified in separate
   documents.

5.14.  Centralized protector mode

   In this framework, it is assumed that the service destination of an
   egress-protected service MUST be dual-homed to two edge routers of an
   MPLS network.  One of them is the protected egress router, and the
   other is a backup egress router.  So far in this document, the
   discussion has been focusing on the scenario where a protector and a
   backup egress router are co-located as one router.  Therefore, the
   number of protectors in a network is equal to the number of backup
   egress routers.  As another scenario, a network may assign a small
   number of routers to serve as dedicated protectors, each protecting a
   subset of egress routers.  These protectors are called centralized
   protectors.

   Topologically, a centralized protector may be decoupled from all
   backup egress routers, or it may be co-located with one backup egress
   router while decoupled from the other backup egress routers.  The
   procedures in this section assume the scenario where a protector and
   a backup egress router are decoupled.




Yimin Shen, et al.       Expires March 24, 2018                [Page 17]


Internet-Draft      MPLS Egress Protection Framework      September 2017


                  services 1, ..., N
        =====================================> tunnel

      I ------ R1 ------- PLR --------------- E ----
   ingress          penultimate-hop        egress    \
                           |  .           (primary    \
                           |  .            service     \
                           |  .            instances)   \
                           |  .                          \
                           |  . bypass                    \   service
                          R2  . tunnel                      destinations
                           |  .                           / (CEs, sites)
                           |  .                          /
                           |  .                         /
                           |  .                        /
                           |  .    tunnel             /
                           |   =============>        /
                           P ---------------- E' ---
                       protector        backup egress
                      (protection          (backup
                       service              service
                       instances)           instances)


                                 Figure 2

   Like a co-located protector, a centralized protector hosts protection
   service instances, receives rerouted service packets from PLRs, and
   performs context label switching and/or context IP forwarding.  For
   each service, instead of sending service packets directly to the
   service destination, the protector MUST send them via another
   transport tunnel to the corresponding backup service instance on a
   backup egress router.  The backup service instance in turn forwards
   them to the service destination.  Specifically, in the case of an
   MPLS service, the protector MUST swap the service label in each
   received service packet to the label of the backup service advertised
   by the backup egress router, and then push a label (or label stack)
   of the transport tunnel.

   In order for a centralized protector to map an egress-protected MPLS
   service to a service hosted on a backup egress router, there MUST be
   a service label distribution protocol session between the backup
   egress router and the protector.  Through this session, the backup
   egress router advertises the service label of the backup service,
   attached with the FEC of the egress-protected service and the context
   ID of the protected egress {E, P}. Based on this information, the
   protector associates the egress-protected service with the backup
   service, resolves or establishes a transport tunnel to the backup



Yimin Shen, et al.       Expires March 24, 2018                [Page 18]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   egress router, and accordingly sets up forwarding state for the label
   of the egress-protected service in the label space of the egress
   router.

   The service label which the backup egress router advertises to the
   protector can be the same as the label which the backup egress router
   advertises to ingress router(s), if and only if the forwarding state
   of the label does not direct service packets towards the protected
   egress router.  Otherwise, the label is not usable for egress
   protection, because it will loop rerouted service packets back to the
   egress router, which MUST be avoided.  In this case, the backup
   egress router MUST advertise a unique service label dedicated for
   egress protection, and set its forwarding state to use the backup
   egress router's connectivity with the service destination.

6.  Egress link protection

   Egress link protection is achievable through similar procedures to
   that of egress node protection.  In normal situations, an egress
   router forwards service packets to a service destination based on a
   service label, whose forwarding state points to an egress link.  In
   egress link protection, the egress router acts as PLR, by performing
   local failure detection and local repair.  Specifically, the egress
   router pre-establishes an egress-protection bypass tunnel to a
   protector, and installs bypass forwarding state for the service
   label, pointing to the bypass tunnel.  During local repair, the
   egress router reroutes service packets via the bypass tunnel to the
   protector.  The protector in turn forwards the packets to the service
   destination (in the co-located protector mode, as shown in Figure-3),
   or forwards the packets first to a backup egress router and then to
   the service destination (in the centralized protector mode, as shown
   in Figure-4).



















Yimin Shen, et al.       Expires March 24, 2018                [Page 19]


Internet-Draft      MPLS Egress Protection Framework      September 2017


                        service
        =====================================> tunnel

      I ------ R1 -------  R2 --------------- E ----
   ingress                 |  ............. egress   \
                           |  .              PLR      \
                           |  .            (primary    \
                           |  .             service     \
                           |  .             instance)    \
                           |  .                           \
                           |  . bypass                        service
                           |  . tunnel                      destination
                           |  .                           / (CE, site)
                           |  .                          /
                           |  .                         /
                           |  .                        /
                           |  .                       /
                           |  ...............        /
                           R3 --------------- P ----
                                          protector
                                         (protection
                                          service
                                          instance)

                                 Figure 3


























Yimin Shen, et al.       Expires March 24, 2018                [Page 20]


Internet-Draft      MPLS Egress Protection Framework      September 2017


                        service
        =====================================> tunnel

      I ------ R1 -------  R2 --------------- E ----
   ingress                 |  ............. egress   \
                           |  .              PLR      \
                           |  .            (primary    \
                           |  .             service     \
                           |  .             instance)    \
                           |  .                           \
                           |  . bypass                        service
                           |  . tunnel                      destination
                           |  .                           / (CE, site)
                           |  .                          /
                           |  .                         /
                           |  .                        /
                           |  .    tunnel             /
                           |   =============>        /
                           R3 --------------- P ----
                       protector        backup egress
                      (protection         (backup
                       service             service
                       instance)           instance)


                                 Figure 4

   There are two approaches to set up the bypass forwarding state on the
   egress router, depending on whether the egress router knows the
   service label advertised by the backup egress router.  The difference
   is that one approach requires the protector to perform context label
   switching, and the other one does not.  Both approaches are equally
   supported by this framework, and may be used in parallel.

      (1) The first approach applies when the egress router does not
      know the service label advertised by the backup egress router.  In
      this case, the egress router sets up the bypass forwarding state
      as a label push with the outgoing label of the egress-protection
      bypass tunnel.  Rerouted packets will have the egress router's
      service label intact.  Therefore, the protector MUST perform
      context label switching, and the bypass tunnel MUST be destined
      for the context ID of the {E, P} and established as described in
      Section 5.11.  This approach is consistent with egress node
      protection.  A protector can serve both egress node protection and
      egress link protection in a consistent manner, and both the co-
      located protector mode and the centralized protector mode may be
      used (Figure-3 and Figure-4).




Yimin Shen, et al.       Expires March 24, 2018                [Page 21]


Internet-Draft      MPLS Egress Protection Framework      September 2017


      (2) The second approach applies when the egress router knows the
      service label advertised by the backup egress route, via a label
      distribution protocol session.  In this case, the backup egress
      router serves as the protector for egress link protection,
      regardless of the protector of egress node protection, which
      should be the same router in the co-located protector mode but may
      be a different router in the centralized protector mode.  The
      egress router sets up the bypass forwarding state as a label swap
      from the incoming service label to the service label of the
      protector, followed by a label push with the outgoing label of the
      egress link protection bypass tunnel.  The bypass tunnel is a
      regular tunnel destined for an IP address of the protector,
      instead of the context ID of the {E, P}. The protector simply
      forwards rerouted service packets based on its own service label,
      rather than performing context label switching.  With this
      approach, only the co-located protector mode is applicable.

   Note that for a bidirectional service, the physical link of an egress
   link may carry service traffic bi-directionally.  Therefore, a
   failure of the physical link may be considered as an egress link
   failure for the traffic towards the service destination, as well as
   an ingress link failure for the traffic in the opposite direction.
   However, protection for ingress link failure SHOULD be provided by a
   separate mechanism, and hence is out of the scope of this framework.

7.  Global repair

   This framework provides a fast but temporary repair for egress node
   and link failures.  For permanent repair, it is RECOMMENDED that the
   traffic SHOULD be moved to an alternative tunnel or alternative
   services which are fully functional.  This is referred to as global
   repair.  Possible triggers of global repair include control plane
   notifications of tunnel and service status, end-to-end OAM and fault
   detection at tunnel or service levels, and others.  The alternative
   tunnel and services may be pre-established as standby, or newly
   established as a result of the triggers or network protocol
   convergence.

8.  Example: Layer-3 VPN egress protection

   This section shows an example of egress protection for a layer-3 VPN.










Yimin Shen, et al.       Expires March 24, 2018                [Page 22]


Internet-Draft      MPLS Egress Protection Framework      September 2017


                           ---------- R1 ----------- PE2 -
                          /          (PLR)          (PLR)  \
    (          )         /            |               |     (          )
    (          )        /             |               |     (          )
    (  site 1  )-- PE1 <              |               R3    (  site 2  )
    (          )        \             |               |     (          )
    (          )         \            |               |     (          )
                          \           |               |    /
                           ---------- R2 ----------- PE3 -
                                                 (protector)


                                 Figure 5

   In this example, the site 1 (subnet 203.0.113.192/26) of a given VPN
   is attached to PE1, and site 2 (subnet 203.0.113.128/26) is dual-
   homed to PE2 and PE3.  PE2 is the primary PE for site 2, and PE3 is
   the backup PE.  Each PE hosts a VPN instance.  R1 and R2 are transit
   routers in the MPLS network.  The network uses OSPF as routing
   protocol, and RSVP-TE as tunnel signaling protocol.  The PEs use BGP
   to exchange VPN prefixes and VPN labels between each other.

   Using the framework in this document, the network assigns PE3 to be a
   protector for PE2 to protect the VPN traffic in the direction from
   site 1 to site 2.  This is the co-located protector mode.  Hence, PE2
   and PE3 form a protected egress {PE2, PE3}. A context ID 198.51.100.1
   is assigned to the protected egress {PE2, PE3}. The VPN instance on
   PE3 serves as a protection instance for the VPN instance on PE2.  On
   PE3, a context label 100 is assigned to the context ID, and a label
   table pe2.mpls is created to represent PE2's label space.  PE3
   installs the label 100 in its default MPLS forwarding table, with
   nexthop pointing to the label table pe2.mpls.  PE2 and PE3 are
   coordinated to use the proxy mode to advertise the context ID in the
   routing domain and the TE domain.

   PE2 uses per-VRF VPN label allocation mode.  It assigns a single
   label 9000 to the VRF of the VPN.  For a given VPN prefix
   203.0.113.128/26 in site 2, PE2 advertises it along with the label
   9000 and other attributes to PE1 and PE3 via BGP.  In particular, the
   NEXT_HOP attribute is set to the context ID 198.51.100.1.

   Similarly, PE3 also uses per-VRF VPN label allocation mode.  It
   assigns a single label 10000 to the VRF of the VPN.  For the VPN
   prefix 203.0.113.128/26 in site 2, PE3 advertises it along with the
   label 10000 and other attributes to PE1 and PE2 via BGP.  In
   particular, the NEXT_HOP attribute is set to an IP address of PE3.





Yimin Shen, et al.       Expires March 24, 2018                [Page 23]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   Upon receipt and acceptance of the BGP advertisement, PE1 uses the
   context ID 198.51.100.1 as destination to compute a TE path for an
   egress-protected tunnel.  The resulted path is PE1->R1->PE2.  PE1
   then uses RSVP to signal the tunnel, with the context ID 198.51.100.1
   as destination, and with the "node protection desired" flag set in
   the SESSION_ATTRIBUTE of RSVP Path message.  Once the tunnel comes
   up, PE1 maps the VPN prefix 203.0.113.128/26 to the tunnel and
   installs a route for the prefix in the corresponding VRF.  The
   route's nexthop is a push with the VPN label 9000, followed by a push
   with the outgoing label of the egress-protected tunnel.

   Upon receipt of the above BGP advertisement from PE2, PE3 (i.e. the
   protector) recognizes the context ID 198.51.100.1 in the NEXT_HOP
   attribute, and installs a route for label 9000 in the label table
   pe2.mpls.  PE3 sets the route's nexthop to a "protection VRF".  This
   protection VRF contains IP routes corresponding to the IP prefixes in
   the dual-homed site 2, including 203.0.113.128/26.  The nexthops of
   these routes MUST be based on PE3's connectivity with site 2, even if
   this connectivity is not the best path in PE3's VRF due to metrics
   (e.g.  MED, local preference, etc.), and MUST NOT use any path
   traversing PE2.  Note that the protection VRF is a logical concept,
   and it may simply be PE3's own VRF if the VRF satisfies the
   requirement.

8.1.  Egress node protection

   R1, i.e. the penultimate-hop router of the egress-protected tunnel,
   serves as the PLR for egress node protection.  Based on the "node
   protection desired" flag and the destination address (i.e. context ID
   198.51.100.1) of the tunnel, R1 computes a bypass path to
   198.51.100.1 while avoiding PE2.  The resulted bypass path is
   R1->R2->PE3.  R1 then signals the path (i.e. egress-protection bypass
   tunnel), with 198.51.100.1 as destination.

   Upon receipt of an RSVP Path message of the egress-protection bypass
   tunnel, PE3 recognizes the context ID 198.51.100.1 as the
   destination, and hence responds with the context label 100 in an RSVP
   Resv message.

   After the egress-protection bypass tunnel comes up, R1 installs a
   bypass nexthop for the egress-protected tunnel.  The bypass nexthop
   is a swap from the incoming label of the egress-protected tunnel to
   the outgoing label of the egress-protection bypass tunnel.

   When R1 detects a failure of PE2, it will invoke the above bypass
   nexthop to reroute VPN service packets.  The packets will have the
   label of the bypass tunnel as outer label, and the VPN label 9000 as
   inner label.  When the packets arrive at PE3, they will have the



Yimin Shen, et al.       Expires March 24, 2018                [Page 24]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   context label 100 as outer label, and the VPN label 9000 as inner
   label.  The context label will first be popped, and then the VPN
   label will be looked up in the label table pe2.mpls.  The lookup will
   cause the VPN label to be popped, and the IP packets will finally be
   forwarded to site 2 based on the protection VRF.

8.2.  Egress link protection

   PE2 serves as the PLR for egress link protection.  It has already
   learned the VPN label 10000 from PE3, and hence it uses the approach
   (2) described in Section 6 to set up bypass forwarding state.  It
   signals an egress-protection bypass tunnel to PE3, by using the path
   PE2->R3->PE3, and PE3's IP address as destination.  After the bypass
   tunnel comes up, PE2 installs a bypass nexthop for the VPN label
   9000.  The bypass nexthop is a label swap from the incoming label
   9000 to the VPN label 10000 of PE3, followed by a label push with the
   outgoing label of the bypass tunnel.

   When PE3 detects a failure of the egress link, it will invoke the
   above bypass nexthop to reroute VPN service packets.  The packets
   will have the label of the bypass tunnel as outer label, and the VPN
   label 10000 as inner label.  When the packets arrive at PE3, the VPN
   label 10000 will be popped, and the IP packets will be forwarded
   based on the VRF indicated by on the VPN label 10000.

8.3.  Global repair

   Eventually, global repair will take effect, as control plane
   protocols converge on the new topology.  PE1 will choose PE3 as new
   entrance to site 2.  Before that happens, the VPN traffic has been
   protected by the above local repair.

9.  IANA Considerations

   This document has no request for new IANA allocation.

10.  Security Considerations

   The framework in this document relies on fast reroute around a
   network failure.  Specifically, service traffic is temporarily
   rerouted from a PLR to a protector.  In the centralized protector
   mode, the traffic is further rerouted from the protector to a backup
   egress router.  Such kind of fast reroute is planned and anticipated,
   and hence it should not be viewed as a new security threat.

   The framework requires a service label distribution protocol to run
   between an egress router and a protector.  The available security




Yimin Shen, et al.       Expires March 24, 2018                [Page 25]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   measures of the protocol MAY be used to achieve a secured session
   between the two routers.

11.  Acknowledgements

   This document leverages work done by Yakov Rekhter, Kevin Wang and
   Zhaohui Zhang on MPLS egress protection.  Thanks to Alexander
   Vainshtein and Rolf Winter for their valuable comments that helped
   shape this document and improve its clarity.

12.  References

12.1.  Normative References

   [SR-ARCH]  Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing (work in progress), 2016.

   [SR-OSPF]  Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions (work in progress), 2016.

   [SR-ISIS]  Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
              Extensions for Segment Routing", draft-ietf-isis-segment-
              routing-extensions (work in progress), 2016.

12.2.  Informative References

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <https://www.rfc-editor.org/info/rfc4090>.

   [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,
              <https://www.rfc-editor.org/info/rfc5286>.

   [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,
              <https://www.rfc-editor.org/info/rfc7490>.







Yimin Shen, et al.       Expires March 24, 2018                [Page 26]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   [RFC7812]  Atlas, A., Bowers, C., and G. Enyedi, "An Architecture for
              IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-
              FRR)", RFC 7812, DOI 10.17487/RFC7812, June 2016,
              <https://www.rfc-editor.org/info/rfc7812>.

   [BGP-PIC]  Bashandy, P., Filsfils, C., and P. Mohapatra, "BGP Prefix
              Independent Convergence", draft-ietf-rtgwg-bgp-pic-05.txt
              (work in progress), 2017.

Authors' Addresses

   Yimin Shen
   Juniper Networks
   10 Technology Park Drive
   Westford, MA  01886
   USA

   Phone: +1 9785890722
   Email: yshen@juniper.net


   Minto Jeyananth
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089
   USA

   Phone: +1 4089367563
   Email: minto@juniper.net


   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   Hannes Gredler
   RtBrick Inc

   Email: hannes@rtbrick.com


   Carsten Michel
   Deutsche Telekom

   Email: c.michel@telekom.de




Yimin Shen, et al.       Expires March 24, 2018                [Page 27]


Internet-Draft      MPLS Egress Protection Framework      September 2017


   Huaimo Chen
   Huawei Technologies Co., Ltd.

   Email: huaimo.chen@huawei.com


   Yuanlong Jiang
   Huawei Technologies Co., Ltd.
   Bantian, Longgang district
   Shenzhen 518129
   China

   Email: jiangyuanlong@huawei.com






































Yimin Shen, et al.       Expires March 24, 2018                [Page 28]