GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc4090

Network Working Group P. Pan, Ed. Request for Comments: 4090 Hammerhead Systems Category: Standards Track G. Swallow, Ed.

                                                         Cisco Systems
                                                         A. Atlas, Ed.
                                                         Avici Systems
                                                              May 2005
         Fast Reroute Extensions to RSVP-TE for LSP Tunnels

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This document defines RSVP-TE extensions to establish backup label-
 switched path (LSP) tunnels for local repair of LSP tunnels.  These
 mechanisms enable the re-direction of traffic onto backup LSP tunnels
 in 10s of milliseconds, in the event of a failure.
 Two methods are defined here.  The one-to-one backup method creates
 detour LSPs for each protected LSP at each potential point of local
 repair.  The facility backup method creates a bypass tunnel to
 protect a potential failure point; by taking advantage of MPLS label
 stacking, this bypass tunnel can protect a set of LSPs that have
 similar backup constraints.  Both methods can be used to protect
 links and nodes during network failure.  The described behavior and
 extensions to RSVP allow nodes to implement either method or both and
 to interoperate in a mixed network.

Pan, et al. Standards Track [Page 1] RFC 4090 RSVP-TE Fast Reroute May 2005

Table of Contents

 1.  Introduction ...................................................3
     1.1.  Background ...............................................4
 2.  Terminology ....................................................4
 3.  Local Repair Techniques ........................................6
     3.1.  One-to-One Backup ........................................6
     3.2.  Facility Backup ..........................................7
 4.  RSVP Extensions ................................................8
     4.1.  FAST_REROUTE Object ......................................8
     4.2.  DETOUR Object ...........................................11
           4.2.1. DETOUR Object for IPv4 Address ...................11
           4.2.2. DETOUR Object for IPv6 Address ...................12
     4.3.  SESSION_ATTRIBUTE Flags .................................13
     4.4.  RRO IPv4/IPv6 Sub-object Flags ..........................14
 5.  Head-End Behavior .............................................15
 6.  Point of Local Repair (PLR) Behavior ..........................16
     6.1.  Signaling a Backup Path .................................17
           6.1.1. Backup Path Identification: Sender
                  Template-Specific ................................19
           6.1.2. Backup Path Identification: Path-Specific ........19
     6.2.  Procedures for Backup Path Computation ..................20
     6.3.  Signaling Backups for One-to-One Protection .............21
           6.3.1. Make-before-Break with Detour LSPs ...............22
           6.3.2. Message Handling .................................23
           6.3.3. Local Reroute of Traffic onto Detour LSP .........23
      6.4. Signaling for Facility Protection .......................24
           6.4.1. Discovering Downstream Labels ....................24
           6.4.2. Procedures for the PLR before Local Repair .......24
           6.4.3. Procedures for the PLR during Local Repair .......25
           6.4.4. Processing Backup Tunnel's ERO ...................26
      6.5. PLR Procedures during Local Repair ......................26
           6.5.1. Notification of Local Repair .....................26
           6.5.2. Revertive Behavior ...............................27
 7.  Merge Node Behavior ...........................................28
     7.1.  Handling Backup Path Messages before Failure ............28
           7.1.1. Merging Backup Paths using the Sender
                  Template-Specific Method .........................29
           7.1.2. Merging Detours using the Path-Specific Method ...29
           7.1.3. Message Handling for Merged Detours ..............31
     7.2.  Handling Failures .......................................31
 8.  Behavior of All LSRs ..........................................32
     8.1.  Merging Detours in the Path-Specific Method .............32
 9.  Security Considerations .......................................33
 10. IANA Considerations ...........................................33
 11. Contributors ..................................................35
 12. Acknowledgments ...............................................36
 13. Normative References ..........................................36

Pan, et al. Standards Track [Page 2] RFC 4090 RSVP-TE Fast Reroute May 2005

1. Introduction

 This document extends RSVP [RSVP] to establish backup label-switched
 path (LSP) tunnels for the local repair of LSP tunnels.  This
 extension will meet the needs of real-time applications such as voice
 over IP, for which user traffic should be redirected onto backup LSP
 tunnels in 10s of milliseconds.  This timing requirement can be
 satisfied by computing and signaling backup LSP tunnels in advance of
 failure and by re-directing traffic as close to the failure point as
 possible.  In this way, the time for redirection includes no path
 computation and no signaling delays, including delays to propagate
 failure notification between label-switched routers (LSRs).  Speed of
 repair is the primary advantage of the methods and extensions
 described here.  The term local repair is used when referring to
 techniques that re-direct traffic to a backup LSP tunnel in response
 to a local failure.
 A protected LSP is an explicitly-routed LSP that is provided with
 protection.  The repair methods described here are applicable only to
 explicitly-routed LSPs.  Application of these methods to LSPs that
 dynamically change their routes, such as LSPs used in unicast IGP
 routing, is beyond the scope of this document.
 Section 2 covers new terminology used in this document.  Section 3
 describes two basic methods for creating backup LSPs.  Section 4
 describes the RSVP protocol extensions to support local protection.
 Section 5 presents the behavior of an LSR that seeks to request local
 protection for an LSP.  The behavior of a potential point of local
 repair (PLR) is given in Section 6, which describes how to determine
 the appropriate strategy for protecting an LSP and how to implement
 each of the strategies.  Section 7 describes the behavior of a merge
 node, the LSR where a protected LSP and its backup LSP rejoin.
 Finally, Section 8 discusses the required behavior of other nodes in
 the network.
 The methods discussed in this document depend upon three assumptions:
    o    An LSR that is on the path of a protected LSP should always
         assume that it is a merge point.  This is necessary because
         the facility backup method does not signal backups through a
         bypass tunnel before failure.
    o    If the one-to-one backup method is used and a DETOUR object
         is included, the LSRs in the traffic-engineered network
         should support the DETOUR object.  This is necessary so that
         the Path message containing the DETOUR object is not
         rejected.

Pan, et al. Standards Track [Page 3] RFC 4090 RSVP-TE Fast Reroute May 2005

    o    Understanding the DETOUR object is required to support the
         path-specific method, which requires that LSRs in the
         traffic-engineered network be capable of merging detours.

1.1. Background

 Several years before work began on this document, operational
 networks had deployed two independent methods of doing fast reroute;
 these methods are called here one-to-one backup and facility backup.
 Vendors trying to support both methods experienced compatibility
 problems in attempting to produce a single implementation capable of
 interoperating with both methods.  There are technical tradeoffs
 between the methods.  These tradeoffs are so topologically dependent
 that the community has not converged on a single approach.
 This document rationalizes the RSVP signaling for both methods so
 that any implementation can recognize all fast reroute requests and
 clearly respond.  The response may be positive if the method can be
 performed, or it may be a clear error to inform the requester to seek
 alternate backup means.  This document also allows a single
 implementation to support both methods, thereby providing a range of
 capabilities.  The described behavior and extensions to RSVP allow
 LERs and LSRs to implement either method or both.
 While the two methods could in principle be used in a single network,
 it is expected that operators will continue to deploy either one or
 the other.  The goal of this document is to standardize the RSVP
 signaling so that a network composed of LSRs that implement both
 methods or a network composed of some LSRs that support one method
 and others that support both can properly signal among those LSRs to
 achieve fast restoration.

2. Terminology

 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 [RFC-WORDS].
 The reader is assumed to be familiar with the terminology in [RSVP]
 and [RSVP-TE].
    LSR: Label-Switch Router.
    LSP: An MPLS Label-Switched Path.  In this document, an LSP will
          always be explicitly routed.
    Local Repair: Techniques used to repair LSP tunnels quickly when a
          node or link along the LSP's path fails.

Pan, et al. Standards Track [Page 4] RFC 4090 RSVP-TE Fast Reroute May 2005

    PLR: Point of Local Repair.  The head-end LSR of a backup tunnel
          or a detour LSP.
    One-to-One Backup: A local repair method in which a backup LSP is
          separately created for each protected LSP at a PLR.
    Facility Backup: A local repair method in which a bypass tunnel is
          used to protect one or more protected LSPs that traverse the
          PLR, the resource being protected, and the Merge Point in
          that order.
    Protected LSP: An LSP is said to be protected at a given hop if it
          has one or multiple associated backup tunnels originating at
          that hop.
    Detour LSP: The LSP that is used to re-route traffic around a
          failure in one-to-one backup.
    Bypass Tunnel: An LSP that is used to protect a set of LSPs
          passing over a common facility.
    Backup Tunnel: The LSP that is used to backup up one of the many
          LSPs in many-to-one backup.
    NHOP Bypass Tunnel: Next-Hop Bypass Tunnel.  A backup tunnel that
          bypasses a single link of the protected LSP.
    NNHOP Bypass Tunnel: Next-Next-Hop Bypass Tunnel.  A backup tunnel
          that bypasses a single node of the protected LSP.
    Backup Path: The LSP that is responsible for backing up one
          protected LSP.  A backup path refers to either a detour LSP
          or a backup tunnel.
    MP: Merge Point.  The LSR where one or more backup tunnels rejoin
          the path of the protected LSP downstream of the potential
          failure.  The same LSR may be both an MP and a PLR
          simultaneously.
    DMP: Detour Merge Point.  In the case of one-to-one backup, this
          is an LSR where multiple detours converge.  Only one detour
          is signaled beyond that LSR.
    Reroutable LSP: Any LSP for which the head-end LSR requests local
          protection.  See Section 5 for more detail.
    CSPF: Constraint-based Shortest Path First.

Pan, et al. Standards Track [Page 5] RFC 4090 RSVP-TE Fast Reroute May 2005

    SRLG Disjoint: A path is considered to be SRLG disjoint from a
          given link or node if the path does not use any links or
          nodes which belong to the same SRLG as that given link or
          node.

3. Local Repair Techniques

 Two different methods for local protection are described.  In the
 one-to-one backup method, a PLR computes a separate backup LSP,
 called a detour LSP, for each LSP that the PLR protects.  In the
 facility backup method, the PLR creates a single bypass tunnel that
 can be used to protect multiple LSPs.

3.1. One-to-One Backup

 In the one-to-one backup method, a label-switched path is established
 that intersects the original LSP somewhere downstream of the point of
 link or node failure.  A separate backup LSP is established for each
 LSP that is backed up.
            [R1]----[R2]----[R3]------[R4]------[R5]
                \       \       \    /    \    /
                 [R6]----[R7]----[R8]------[R9]
            Protected LSP:  [R1->R2->R3->R4->R5]
            R1's Backup:    [R1->R6->R7->R8->R3]
            R2's Backup:    [R2->R7->R8->R4]
            R3's Backup:    [R3->R8->R9->R5]
            R4's Backup:    [R4->R9->R5]
            Example 1.  One-to-One Backup Technique
 In the simple topology shown in Example 1, the protected LSP runs
 from R1 to R5.  R2 can provide user traffic protection by creating a
 partial backup LSP that merges with the protected LSP at R4.  We
 refer to a partial one-to-one backup LSP [R2->R7->R8->R4] as a
 detour.
 To protect an LSP that traverses N nodes fully, there could be as
 many as (N - 1) detours.  Example 1 shows the paths for the detours
 necessary to protect fully the LSP in the example.  To minimize the
 number of LSPs in the network, it is desirable to merge a detour back
 to its protected LSP, when feasible.  When a detour LSP intersects
 its protected LSP at an LSR with the same outgoing interface, it will
 be merged.

Pan, et al. Standards Track [Page 6] RFC 4090 RSVP-TE Fast Reroute May 2005

 When a failure occurs along the protected LSP, the PLR redirects
 traffic onto the local detour.  For instance, if the link [R2->R3]
 fails in Example 1, R2 will switch traffic received from R1 onto the
 protected LSP along link [R2->R7], using the label received when R2
 created the detour.  When R4 receives traffic with the label provided
 for R2's detour, R4 will switch that traffic onto link [R4-R5], using
 the label received from R5 for the protected LSP.  At no point does
 the depth of the label stack increase as a result of the detour.
 While R2 is using its detour, traffic will take the path
 [R1->R2->R7->R8->R4->R5].

3.2. Facility Backup

 The facility backup method takes advantage of the MPLS label stack.
 Instead of creating a separate LSP for every backed-up LSP, a single
 LSP is created that serves to back up a set of LSPs.  We call such an
 LSP tunnel a bypass tunnel.
 The bypass tunnel must intersect the path of the original LSP(s)
 somewhere downstream of the PLR.  Naturally, this constrains the set
 of LSPs being backed up via that bypass tunnel to those that pass
 through some common downstream node.  All LSPs that pass through the
 point of local repair and through this common node that do not also
 use the facilities involved in the bypass tunnel are candidates for
 this set of LSPs.
               [R8]
                   \
             [R1]---[R2]----[R3]-----[R4]---[R5]
                        \           /    \
                         [R6]===[R7]      [R9]
              Protected LSP 1:   [R1->R2->R3->R4->R5]
              Protected LSP 2:   [R8->R2->R3->R4]
              Protected LSP 3:   [R2->R3->R4->R9]
              Bypass LSP Tunnel: [R2->R6->R7->R4]
                  Example 2.  Facility Backup Technique
 In Example 2, R2 has built a bypass tunnel that protects against the
 failure of link [R2->R3] and node [R3].  The doubled lines represent
 this tunnel.  This technique provides a scalability improvement, in
 that the same bypass tunnel can also be used to protect LSPs from any
 of R1, R2, or R8 to any of R4, R5, or R9.  Example 2 describes three
 different protected LSPs that are using the same bypass tunnel for
 protection.

Pan, et al. Standards Track [Page 7] RFC 4090 RSVP-TE Fast Reroute May 2005

 As with the one-to-one method, there could be as many as (N-1) bypass
 tunnels to fully protect an LSP that traverses N nodes.  However,
 each of those bypass tunnels could protect a set of LSPs.
 When a failure occurs along a protected LSP, the PLR redirects
 traffic into the appropriate bypass tunnel.  For instance, if link
 [R2->R3] fails in Example 2, R2 will switch traffic received from R1
 on the protected LSP onto link [R2->R6].  The label will be switched
 for one which will be understood by R4 to indicate the protected LSP,
 and the bypass tunnel's label will then be pushed onto the label-
 stack of the redirected packets.  If penultimate-hop-popping is used,
 the merge point in Example 2, R4, will receive the redirected packet
 with a label indicating the protected LSP that the packet is to
 follow.  If penultimate-hop-popping is not used, R4 will pop the
 bypass tunnel's label and examine the label underneath to determine
 the protected LSP that the packet is to follow.  When R2 is using the
 bypass tunnel for protected LSP 1, the traffic takes the path
 [R1->R2->R6->R7->R4->R5]; the bypass tunnel is the connection between
 R2 and R4.

4. RSVP Extensions

 This specification defines two additional objects, FAST_REROUTE and
 DETOUR, to extend RSVP-TE for fast-reroute signaling.  These new
 objects are backward compatible with LSRs that do not recognize them
 (see section 3.10 in [RSVP]).  Both objects can only be carried in
 RSVP Path messages.
 The SESSION_ATTRIBUTE and RECORD_ROUTE objects are also extended to
 support bandwidth and node protection features.

4.1. FAST_REROUTE Object

 The FAST_REROUTE object is used to control the backup used for the
 protected LSP.  This specifies the setup and hold priorities, session
 attribute filters, and bandwidth to be used for protection.  It also
 allows a specific local protection method to be requested.  This
 object MUST only be inserted into the PATH message by the head-end
 LER and MUST NOT be changed by downstream LSRs.  The FAST_REROUTE
 object has the following format:

Pan, et al. Standards Track [Page 8] RFC 4090 RSVP-TE Fast Reroute May 2005

    Class-Num = 205
    C-Type = 1
           0             1             2             3
    +-------------+-------------+-------------+-------------+
    |       Length (bytes)      |  Class-Num  |   C-Type    |
    +-------------+-------------+-------------+-------------+
    | Setup Prio  | Hold Prio   | Hop-limit   |    Flags    |
    +-------------+-------------+-------------+-------------+
    |                  Bandwidth                            |
    +-------------+-------------+-------------+-------------+
    |                  Include-any                          |
    +-------------+-------------+-------------+-------------+
    |                  Exclude-any                          |
    +-------------+-------------+-------------+-------------+
    |                  Include-all                          |
    +-------------+-------------+-------------+-------------+
    Setup Priority
       The priority of the backup path with respect to taking
       resources, in the range 0 to 7.  The value 0 is the highest
       priority.  Setup Priority is used in deciding whether this
       session can preempt another session.  See [RSVP-TE] for the
       usage on priority.
    Holding Priority
       The priority of the backup path with respect to holding
       resources, in the range 0 to 7.  The value 0 is the highest
       priority.  Holding Priority is used in deciding whether this
       session can be preempted by another session.  See [RSVP-TE] for
       the usage on priority.
    Hop-limit
       The maximum number of extra hops the backup path is allowed to
       take, from current node (a PLR) to an MP, with PLR and MP
       excluded from the count.  For example, hop-limit of 0 means
       that only direct links between PLR and MP can be considered.
    Flags
       0x01  One-to-One Backup Desired
          Requests protection via the one-to-one backup method.

Pan, et al. Standards Track [Page 9] RFC 4090 RSVP-TE Fast Reroute May 2005

       0x02  Facility Backup Desired
          Requests protection via the facility backup method.
    Bandwidth
       Bandwidth estimate; 32-bit IEEE floating point integer, in
       bytes per second.
    Exclude-any
       A 32-bit vector representing a set of attribute filters
       associated with a backup path, any of which renders a link
       unacceptable.
    Include-any
       A 32-bit vector representing a set of attribute filters
       associated with a backup path, any of which renders a link
       acceptable (with respect to this test).  A null set (all bits
       set to zero) automatically passes.
    Include-all
       A 32-bit vector representing a set of attribute filters
       associated with a backup path, all of which must be present for
       a link to be acceptable (with respect to this test).  A null
       set (all bits set to zero) automatically passes.
 The two high-order bits of the Class-Num (11) cause nodes that do not
 understand the object to ignore it and pass it forward unchanged.
 For informational purposes, a different C-Type value and format for
 the FAST_REROUTE object are specified below.  This is used by legacy
 implementations.  The meaning of the fields is the same as that
 described for C-Type 1.

Pan, et al. Standards Track [Page 10] RFC 4090 RSVP-TE Fast Reroute May 2005

    Class-Num = 205
    C-Type = 7
           0             1             2             3
    +-------------+-------------+-------------+-------------+
    |       Length (bytes)      |  Class-Num  |   C-Type    |
    +-------------+-------------+-------------+-------------+
    | Setup Prio  | Hold Prio   | Hop-limit   | Reserved    |
    +-------------+-------------+-------------+-------------+
    |                  Bandwidth                            |
    +-------------+-------------+-------------+-------------+
    |                  Include-any                          |
    +-------------+-------------+-------------+-------------+
    |                  Exclude-any                          |
    +-------------+-------------+-------------+-------------+
 Unknown C-Types should be treated as specified in [RSVP] Section
 3.10.

4.2. DETOUR Object

 The DETOUR object is used in the one-to-one backup method to identify
 detour LSPs.

4.2.1. DETOUR Object for IPv4 Address

    Class-Num = 63
    C-Type = 7
          0             1              2             3
     +-------------+-------------+-------------+-------------+
     |       Length (bytes)      |  Class-Num  |   C-Type    |
     +-------------+-------------+-------------+-------------+
     |                      PLR_ID  1                        |
     +-------------+-------------+-------------+-------------+
     |                    Avoid_Node_ID 1                    |
     +-------------+-------------+-------------+-------------+
    //                        ....                          //
     +-------------+-------------+-------------+-------------+
     |                      PLR_ID  n                        |
     +-------------+-------------+-------------+-------------+
     |                    Avoid_Node_ID  n                   |
     +-------------+-------------+-------------+-------------+
    PLR_ID  (1 - n)
       IPv4 address identifying the PLR that is the beginning point of
       the detour.  Any local address on the PLR can be used.

Pan, et al. Standards Track [Page 11] RFC 4090 RSVP-TE Fast Reroute May 2005

    Avoid_Node_ID  (1 - n)
       IPv4 address identifying the immediate downstream node that the
       PLR is trying to avoid.  Any local address of the downstream
       node can be used.  This field is mandatory and is used by the
       MP for the merging rules discussed below.

4.2.2. DETOUR Object for IPv6 Address

    Class-Num = 63
    C-Type = 8
           0             1              2             3
      +-------------+-------------+-------------+-------------+
      |       Length (bytes)      |  Class-Num  |   C-Type    |
      +-------------+-------------+-------------+-------------+
      |                      PLR_ID  1                        |
      +-------------+-------------+-------------+-------------+
      |                      PLR_ID  1 (continued)            |
      +-------------+-------------+-------------+-------------+
      |                      PLR_ID  1 (continued)            |
      +-------------+-------------+-------------+-------------+
      |                      PLR_ID  1 (continued)            |
      +-------------+-------------+-------------+-------------+
      |                    Avoid_Node_ID 1                    |
      +-------------+-------------+-------------+-------------+
      |                    Avoid_Node_ID 1 (continued)        |
      +-------------+-------------+-------------+-------------+
      |                    Avoid_Node_ID 1 (continued)        |
      +-------------+-------------+-------------+-------------+
      |                    Avoid_Node_ID 1 (continued)        |
      +-------------+-------------+-------------+-------------+
     //                        ....                          //
      +-------------+-------------+-------------+-------------+
    PLR_ID  (1 - n)
       An IPv6 128-bit unicast host address identifying the PLR that
       is the beginning point of the detour.  Any local address on the
       PLR can be used.
    Avoid_Node_ID  (1 - n)
       An IPv6 128-bit unicast host address identifying the immediate
       downstream node that the PLR is trying to avoid.  Any local
       address on the downstream node can be used.  This field is

Pan, et al. Standards Track [Page 12] RFC 4090 RSVP-TE Fast Reroute May 2005

       mandatory and is used by the MP for the merging rules discussed
       below.
 There can be more than one pair of (PLR_ID, Avoid_Node_ID) entries in
 a DETOUR object.  If detour merging is desired, after each merging
 operation, the Detour Merge Point should combine all the merged
 detours in subsequent Path messages.
 The high-order bit of the Class-Num is zero; LSRs that do not support
 the DETOUR objects MUST reject any Path message containing a DETOUR
 object and send a PathErr to notify the PLR.  This PathErr SHOULD be
 generated as specified in [RSVP] for unknown objects with a Class-Num
 of the form "0bbbbbbb".
 Unknown C-Types should be treated as specified in [RSVP] Section
 3.10.

4.3. SESSION_ATTRIBUTE Flags

 To request bandwidth and node protection explicitly, two new flags
 are defined in the SESSION_ATTRIBUTE object.
 For both C-Type 1 and 7, the SESSION_ATTRIBUTE object currently has
 the following flags defined [RSVP-TE]:
    Local protection desired:   0x01
       This flag permits transit routers to use a local repair
       mechanism that may result in violation of the explicit route
       object.  When a fault is detected on an adjacent downstream
       link or node, a transit node may reroute traffic for fast
       service restoration.
    Label recording desired:   0x02
       This flag indicates that label information should be included
       when doing a route record.
    SE Style desired:   0x04
       This flag indicates that the tunnel ingress node may choose to
       reroute this tunnel without tearing it down.  A tunnel egress
       node SHOULD use the SE Style when responding with a Resv
       message.  When requesting fast reroute, the head-end LSR SHOULD
       set this flag; this is not necessary for the path-specific
       method of the one-to-one backup method.

Pan, et al. Standards Track [Page 13] RFC 4090 RSVP-TE Fast Reroute May 2005

 The following new flags are defined:
    Bandwidth protection desired:  0x08
       This flag indicates to the PLRs along the protected LSP path
       that a backup path with a bandwidth guarantee is desired.  The
       bandwidth to be guaranteed is that of the protected LSP, if no
       FAST_REROUTE object is included in the PATH message; if a
       FAST_REROUTE object is in the PATH message, then the bandwidth
       specified therein is to be guaranteed.
    Node protection desired: 0x10
       This flag indicates to the PLRs along a protected LSP path that
       a backup path that bypasses at least the next node of the
       protected LSP is desired.

4.4. RRO IPv4/IPv6 Sub-object Flags

 To report whether bandwidth and/or node protection are provided as
 requested, we define two new flags in the RRO IPv4 sub-object.
 The RRO IPv4 and IPv6 address sub-objects currently have the
 following flags defined [RSVP-TE]:
    Local protection available:  0x01
       Indicates that the link downstream of this node is protected
       via a local repair mechanism, which can be either one-to-one or
       facility backup.
    Local protection in use:  0x02
       Indicates that a local repair mechanism is in use to maintain
       this tunnel (usually in the face of an outage of the link it
       was previously routed over, or an outage of the neighboring
       node).
 Two new flags are defined:
    Bandwidth protection:  0x04
       The PLR will set this bit when the protected LSP has a backup
       path that is guaranteed to provide the desired bandwidth that
       is specified in the FAST_REROUTE object or the bandwidth of the
       protected LSP, if no FAST_REROUTE object was included.  The PLR
       may set this whenever the desired bandwidth is guaranteed; the
       PLR MUST set this flag when the desired bandwidth is guaranteed

Pan, et al. Standards Track [Page 14] RFC 4090 RSVP-TE Fast Reroute May 2005

       and the "bandwidth protection desired" flag was set in the
       SESSION_ATTRIBUTE object.  If the requested bandwidth is not
       guaranteed, the PLR MUST NOT set this flag.
    Node protection:  0x08
       The PLR will set this bit when the protected LSP has a backup
       path that provides protection against a failure of the next LSR
       along the protected LSP.  The PLR may set this whenever node
       protection is provided by the protected LSP's backup path; the
       PLR MUST set this flag when the node protection is provided and
       the "node protection desired" flag was set in the
       SESSION_ATTRIBUTE object.  If node protection is not provided,
       the PLR MUST NOT set this flag.  Thus, if a PLR could only set
       up a link-protection backup path, the "Local protection
       available" bit will be set, but the "Node protection" bit will
       be cleared.

5. Head-End Behavior

 The head-end of an LSP determines whether local protection should be
 requested for that LSP and which local protection method is desired
 for the protected LSP.  The head-end also determines what constraints
 should be requested for the backup paths of a protected LSP.
 To indicate that an LSP should be locally protected, the head-end LSR
 MUST either set the "local protection desired" flag in the
 SESSION_ATTRIBUTE object or include a FAST_REROUTE object in the PATH
 message, or both.  The "local protection desired" flag in the
 SESSION_ATTRIBUTE object SHOULD always be set.  If a head-end LSR
 signals a FAST_REROUTE object, it MUST be stored for Path refreshes.
 The head-end LSR of a protected LSP MUST set the "label recording
 desired" flag in the SESSION_ATTRIBUTE object.  This facilitates the
 use of the facility backup method.  If node protection is desired,
 the head-end LSR should set the "node protection desired" flag in the
 SESSION_ATTRIBUTE object; otherwise, this flag should be cleared.
 Similarly, if a guarantee of bandwidth protection is desired, then
 the "bandwidth protection desired" flag in the SESSION_ATTRIBUTE
 object should be set; otherwise, this flag should be cleared.  If the
 head-end LSR determines that control of the backup paths for the
 protected LSP is desired, then the LSR should include the
 FAST_REROUTE object.  The PLRs will use the attribute filters,
 bandwidth, hop-limit, and priorities to determine the backup paths.
 If the head-end LSR desires that the one-to-one backup method be used
 for the protected LSP, then the head-end LSR should include a
 FAST_REROUTE object and set the "one-to-one backup desired" flag.  If

Pan, et al. Standards Track [Page 15] RFC 4090 RSVP-TE Fast Reroute May 2005

 the head-end LSR desires that the protected LSP be protected via the
 facility backup method, then the head-end LSR should include a
 FAST_REROUTE object and set the "facility backup desired" flag.  The
 lack of a FAST_REROUTE object, or having both these flags clear,
 should be treated by PLRs as a lack of preference.  If both flags are
 set, a PLR may use either method or both.
 The head-end LSR of a protected LSP MUST support the additional flags
 defined in Section 4.4 being set or clear in the RRO IPv4 and IPv6
 sub-objects.  The head-end LSR of a protected LSP MUST support the
 RRO Label sub-object.
 If the head-end LSR of an LSP determines that local protection is
 newly desired, this SHOULD be signaled via make-before-break.

6. Point of Local Repair (PLR) Behavior

 Every LSR along a protected LSP (except the egress) MUST follow the
 PLR behavior described in this document.
 A PLR SHOULD support the FAST_REROUTE object, the "local protection
 desired", "label recording desired", "node protection desired", and
 "bandwidth protection desired" flags in the SESSION_ATTRIBUTE object,
 and the "local protection available", "local protection in use",
 "bandwidth protection", and "node protection" flags in the RRO IPv4
 and IPv6 sub-objects.  A PLR MAY support the DETOUR object.
 A PLR MUST consider an LSP to have asked for local protection if the
 "local protection desired" flag is set in the SESSION_ATTRIBUTE
 object and/or the FAST_REROUTE object is included.  If the
 FAST_REROUTE object is included, a PLR SHOULD consider providing
 one-to-one protection if the "one-to-one desired" is set, and it
 SHOULD consider providing facility backup if the "facility backup
 desired" flag is set.  If the "node protection desired" flag is set,
 the PLR SHOULD try to provide node protection; if this is not
 feasible, the PLR SHOULD then try to provide link protection.  If the
 "bandwidth protection guaranteed" flag is set, the PLR SHOULD try to
 provide a bandwidth guarantee; if this is not feasible, the PLR
 SHOULD then try to provide a backup without a guarantee of the full
 bandwidth.

Pan, et al. Standards Track [Page 16] RFC 4090 RSVP-TE Fast Reroute May 2005

 The following treatment for the RRO IPv4 or IPv6 sub-object's flags
 must be followed if an RRO is included in the protected LSP's RESV
 message.  Based on this additional information, the head-end may take
 appropriate actions.
  1. Until a PLR has a backup path available, the PLR MUST clear the

relevant four flags in the corresponding RRO IPv4 or IPv6 sub-

    object.
  1. Whenever the PLR has a backup path available, the PLR MUST set the

"local protection available" flag. If no established one-to-one

    backup LSP or bypass tunnel exists, or if the one-to-one LSP and
    the bypass tunnel is in "DOWN" state, the PLR MUST clear the
    "local protection available" flag in its IPv4 (or IPv6) address
    sub-object of the RRO and SHOULD send the updated RESV.
  1. The PLR MUST clear the "local protection in use" flag unless it is

actively redirecting traffic into the backup path instead of along

    the protected LSP.
  1. The PLR SHOULD also set the "node protection" flag if the backup

path protects against the failure of the immediate downstream

    node, and, if the path does not, the PLR SHOULD clear the "node
    protection" flag.  This MUST be done if the "node protection
    desired" flag was set in the SESSION_ATTRIBUTE object.
  1. The PLR SHOULD set the "bandwidth protection" flag if the backup

path offers a bandwidth guarantee, and, if the path does not, the

    PLR SHOULD clear the "bandwidth protection" flag.  This MUST be
    done if the "bandwidth protection desired" flag was set in the
    SESSION_ATTRIBUTE object.

6.1. Signaling a Backup Path

 A number of objectives must be met to obtain a satisfactory signaling
 solution.  These are summarized as follows:
    1. Unambiguously and uniquely identifying backup paths.
    2. Unambiguously associating protected LSPs with their backup
       paths.
    3. Working with both global and non-global label spaces.
    4. Allowing merging of backup paths.
    5. Maintaining RSVP state during and after fail-over.

Pan, et al. Standards Track [Page 17] RFC 4090 RSVP-TE Fast Reroute May 2005

 LSP tunnels are identified by a combination of the SESSION and
 SENDER_TEMPLATE objects [RSVP-TE].  The relevant fields are as
 follows.
    IPv4 (or IPv6) tunnel end point address
       IPv4 (or IPv6) address of the egress node for the tunnel.
    Tunnel ID
       A 16-bit identifier used in the SESSION that remains constant
       over the life of the tunnel.
    Extended Tunnel ID
       A 32-bit (IPv4) or 128-bit (IPv6) identifier used in the
       SESSION that remains constant over the life of the tunnel.
       Normally it is set to all zero.  Ingress nodes that wish to
       narrow the scope of a SESSION to the ingress-egress pair may
       place their IP address here as a globally unique identifier.
    IPv4 (or IPv6) tunnel sender address
       IPv4 (or IPv6) address for a sender node.
    LSP ID
       A 16-bit identifier used in the SENDER_TEMPLATE and the
       FILTER_SPEC, which can be changed to allow a sender to share
       resources with itself.
 The first three of these are in the SESSION object and are the basic
 identification for the tunnel.  Setting the "Extended Tunnel ID" to
 an IP address of the head-end LSR allows the scope of the SESSION to
 be narrowed to only LSPs sent by that LSR.  A backup LSP is
 considered part of the same session as its protected LSP; therefore
 these three cannot be varied.
 The last two are in the SENDER_TEMPLATE.  Multiple LSPs in the same
 SESSION may be protected and may take different routes; this is
 common when a tunnel is rerouted using make-before-break.  A backup
 path must be clearly identified with its protected LSP to allow
 correct merging and state treatment.  Therefore, a backup path must
 inherit its LSP ID from the associated protected LSP.  Thus, the only
 field in the SESSION and SENDER_TEMPLATE objects that could be varied
 between a backup path and a protected LSP is the "IPv4 (or IPv6)
 tunnel sender address" in the SENDER_TEMPLATE.

Pan, et al. Standards Track [Page 18] RFC 4090 RSVP-TE Fast Reroute May 2005

 There are two different methods to uniquely identify a backup path,
 described below.

6.1.1. Backup Path Identification: Sender Template-Specific

 In this approach, the SESSION object and the LSP_ID are copied from
 the protected LSP.  The "IPv4 tunnel sender address" is set to an
 address of the PLR.  If the head-end of a tunnel is also acting as
 the PLR, it MUST choose an IP address different from the one used in
 the SENDER_TEMPLATE of the original LSP tunnel.
 When the sender template-specific approach is used, the protected
 LSPs and the backup paths SHOULD use the Shared Explicit (SE) style.
 This allows bandwidth sharing between multiple backup paths.  The
 backup paths and the protected LSP MAY be merged by the Detour Merge
 Points, when the ERO from the MP to the egress is the same on each
 LSP to be merged, as specified in [RSVP-TE].

6.1.2. Backup Path Identification: Path-Specific

 In this approach, rather than vary the SESSION or SENDER_TEMPLATE
 objects, an implementation uses a new object, the DETOUR object, to
 distinguish between PATH messages for a backup path and the protected
 LSP.
 Thus, the backup paths use the same SESSION and SENDER_TEMPLATE
 objects as the ones used in the protected LSP.  The presence of a
 DETOUR object in Path messages signifies a backup path; the presence
 of a FAST_REROUTE object and/or the "local protection requested" flag
 in the SESSION_ATTRIBUTE object indicates a protected LSP.
 In the path message-specific approach, an LSR merges Path messages
 that are received with the same SESSION and SENDER_TEMPLATE objects
 and that also have the same next-hop object.  Without this behavior,
 it would be impossible to associate the multiple RESV messages with
 the backup paths.  However, this merging behavior reduces the total
 number of RSVP states inside the network at the expense of merging
 LSPs with different EROs.

Pan, et al. Standards Track [Page 19] RFC 4090 RSVP-TE Fast Reroute May 2005

6.2. Procedures for Backup Path Computation

 Before a PLR can create a detour or a bypass tunnel, the desired
 explicit route must be determined.  This can be done using a CSPF
 (Constraint-based Shortest Path First) computation.  Before this CSPF
 computation, the following information must be collected at a PLR:
  1. The list of downstream nodes that the protected LSP passes

through. This information is readily available from the

      RECORD_ROUTE objects during LSP setup.  This information is also
      available from the ERO.  However, if the ERO contains loose
      sub-objects, the ERO may not provide adequate information.
  1. The downstream links/nodes that we want to protect against.

Once again, this information is learned from the RECORD_ROUTE

      objects.  Whether node protection is desired is determined by
      the "node protection" flag in the SESSION_ATTRIBUTE object and
      local policy.
  1. The upstream uni-directional links that the protected LSP passes

through. This information is learned from the RECORD_ROUTE

      objects; it is only needed for setting up one-to-one protection.
      In the path-specific method, it is necessary to avoid the detour
      and the protected LSP sharing a common next-hop upstream of the
      failure.  In the sender template-specific mode, this same
      restriction is necessary to avoid sharing bandwidth between the
      detour and its protected LSP, where that bandwidth has been
      reserved only once.
  1. The link attribute filters to be applied. These are derived

from the FAST_REROUTE object, if it is included in the PATH

      message, or from the SESSION_ATTRIBUTE object otherwise.
  1. The bandwidth to be used is found in the FAST_REROUTE object, if

it is included in the PATH message, or in the SESSION_ATTRIBUTE

      object otherwise.  Local policy may modify the bandwidth to be
      reserved.
  1. The hop-limit, if a FAST_REROUTE object was included in the PATH

message.

 When a CSPF algorithm is used to compute the backup route, the
 following constraints must be satisfied:
  1. For detour LSPs, the destination MUST be the tail-end of the

protected LSP. For bypass tunnels (Section 7), the destination

      MUST be the address of the MP.

Pan, et al. Standards Track [Page 20] RFC 4090 RSVP-TE Fast Reroute May 2005

  1. When one-to-one protection is set up by using the path-specific

method, a detour MUST not traverse the upstream links of the

      protected LSP in the same direction.  This prevents the
      possibility of early merging of the detour into the protected
      LSP.  When one-to-one protection is set up using the sender-
      template-specific method, a detour should not traverse the
      upstream links of the protected LSP in the same direction.  This
      prevents sharing the bandwidth between a protected LSP and its
      backup upstream of the failure where the bandwidth would be used
      twice in the event of a failure.
  1. The backup LSP cannot traverse the downstream node and/or link

whose failure is being protected against. Note that if the PLR

      is the penultimate hop, node protection is not possible, and
      only the downstream link can be avoided.  The backup path may be
      computed to be SRLG disjoint from the downstream node and/or
      link being avoided.
  1. The backup path must satisfy the resource requirements of the

protected LSP. This includes the link attribute filters,

      bandwidth, and hop limits determined from the FAST_REROUTE
      object and the SESSION_ATTRIBUTE object.
 If such computation succeeds, the PLR should attempt to establish a
 backup path.  The PLR may schedule a re-computation at a later time
 to discover better paths that might have emerged.  If for any reason,
 the PLR is unable to bring up a backup path, it must schedule a retry
 at a later time.

6.3. Signaling Backups for One-to-One Protection

 Once a PLR has decided to protect an LSP locally with one-to-one
 backup and has identified the desired path, it signals for the
 detour.
 The following describes the transformation to be performed upon the
 protected LSP's PATH message to create the detour LSP's PATH message.
  1. If the sender template-specific method is to be used, then the

PLR MUST change the "IPv4 (or IPv6) tunnel sender address" of

      the SENDER_TEMPLATE to an address belonging to the PLR that is
      not the same as that used for the protected LSP.  Additionally,
      the DETOUR object MAY be added to the PATH message.
  1. If the path-specific method is to be used, then the PLR MUST add

a DETOUR object to the PATH message.

Pan, et al. Standards Track [Page 21] RFC 4090 RSVP-TE Fast Reroute May 2005

  1. The SESSION_ATTRIBUTE flags "Local protection desired",

"Bandwidth protection desired", and "Node protection desired"

      MUST be cleared.  The "Label recording desired" flag MAY be
      modified.  If the Path Message contained a FAST_REROUTE object
      and the ERO is not completely strict, the Include-any, Exclude-
      any, and Include-all fields of the FAST_REROUTE object SHOULD be
      copied to the corresponding fields of the SESSION_ATTRIBUTE
      object.
  1. If the protected LSP's Path message contained a FAST_REROUTE

object, this object MUST be removed from the detour LSP's PATH

      message.
  1. The PLR MUST generate an EXPLICIT_ROUTE object toward the

egress. First, the PLR must remove all sub-objects preceding

      the first address belonging to the Merge Point.  Then the PLR
      SHOULD add sub-objects corresponding to the desired backup path
      between the PLR and the MP.
  1. The SENDER_TSPEC object SHOULD contain the bandwidth information

from the received FAST_REROUTE object, if included in the

      protected LSP's PATH message.
  1. The RSVP_HOP object containing one of the PLR's IP address.
  1. The detour LSPs MUST use the same reservation style as the

protected LSP. This must be correctly reflected in the

      SESSION_ATTRIBUTE object.
   Detour LSPs operate like regular LSPs.  Once a detour path is
   successfully computed and the detour LSP is established, the PLR
   need not compute detour routes again, unless (1) the contents of
   FAST_REROUTE have changed or (2) the downstream interface and/or
   the nexthop router for a protected LSP has changed.  The PLR may
   recompute detour routes at any time.

6.3.1. Make-before-Break with Detour LSPs

 If the sender template-specific method is used, it is possible to do
 make-before-break with detour LSPs.  This is done using two different
 IP addresses belonging to the PLR (which were not used in the
 SENDER_TEMPLATE of the protected LSP).  If the current detour LSP
 uses the first IP address in its SENDER_TEMPLATE, then the new detour
 LSP should be signaled by using the second IP address in its
 SENDER_TEMPLATE.  Once the new detour LSP has been created, the
 current detour LSP can be torn down.  By alternating the use of these
 IP addresses, the current and new detour LSPs will have different
 SENDER_TEMPLATES and, thus, different state in the downstream LSRs.

Pan, et al. Standards Track [Page 22] RFC 4090 RSVP-TE Fast Reroute May 2005

 This make-before-break mechanism, which changes the PLR IP address in
 the DETOUR object instead, is not feasible with the path-specific
 method, as the PATH messages for new and current detour LSPs may be
 merged if they share a common next-hop.

6.3.2. Message Handling

 LSRs must process the detour LSPs independently of the protected LSPs
 to avoid triggering the LSP loop detection procedure described in
 [RSVP-TE].
 The PLR MUST not mix the messages for the protected and the detour
 LSPs.  When a PLR receives Resv, ResvTear, and PathErr messages from
 the downstream detour destination, the messages MUST not be forwarded
 upstream.  Similarly, when a PLR receives ResvErr and ResvConf
 messages from a protected LSP, it MUST not propagate them onto the
 associated detour LSP.
 A session tear-down request is normally originated by the sender via
 PathTear messages.  When a PLR node receives a PathTear message from
 upstream, it MUST delete both the protected and the detour LSPs.  The
 PathTear messages MUST propagate to both protected and detour LSPs.
 During error conditions, the LSRs may send ResvTear messages to fix
 problems on the failing path.  When a PLR node receives the ResvTear
 messages from downstream for a protected LSP, as long as a detour is
 up, the ResvTear messages MUST not be sent further upstream.
 PathErrs should be treated similarly.

6.3.3. Local Reroute of Traffic onto Detour LSP

 When the PLR detects a failure on the protected LSP, the PLR MUST
 rapidly switch packets to the protected LSP's backup LSP instead of
 to the protected LSP's normal out-segment.  The goal of this method
 is to effect the redirection within 10s of milliseconds.
             L32      L33      L34      L35
         R1-------R2-------R3-------R4-------R5
                  |                 |
             L46  |                 | L44
                  |       L47       |
                  R6----------------R7
          Protected LSP: [R1->R2->R3->R4->R5]
          Detour LSP:    [R2->R6->R7->R4]
               Example 3.  Redirect to Detour

Pan, et al. Standards Track [Page 23] RFC 4090 RSVP-TE Fast Reroute May 2005

 In Example 3, if the link [R2->R3] fails, R2 would do the following.
 Any traffic received on link [R1->R2] with label L32 would be sent on
 link [R2->R6] with label L46 (along the detour LSP) instead of on
 link [R3->R4] with label L34 (along the protected LSP).  The merge
 point R4 would recognize that packets received on link [R7->R4] with
 label L44 should be sent on link [R4->R5] with label L35 and that
 they should be merged with the protected LSP.

6.4. Signaling for Facility Protection

 A PLR may use one or more bypass tunnels to protect against the
 failure of a link and/or a node.  These bypass tunnels may be set up
 in advance or may be dynamically created as new protected LSPs are
 signaled.

6.4.1. Discovering Downstream Labels

 To support facility backup, the PLR must determine a label that will
 indicate to the MP that packets received with that label should be
 switched along the protected LSP.  This can be done without
 explicitly signaling the backup path if the MP uses a label space
 global to that LSR.
 As described in Section 6, the head-end LSR MUST set the "label
 recording requested" flag in the SESSION_ATTRIBUTE object for LSPs
 requesting local protection.  This will cause (as specified in
 [RSVP-TE]) all LSRs to record their INBOUND labels and to note via a
 flag whether the label is global to the LSR.  Thus, when a protected
 LSP is first signaled through a PLR, the PLR can examine the RRO in
 the Resv message and learn about the incoming labels that are used by
 all downstream nodes for this LSP
 When MPs use per-interface label spaces, the PLR must send Path
 messages (for each protected LSP using a bypass tunnel) via that
 bypass tunnel prior to the failure in order to discover the
 appropriate MP label.  The signaling procedures for this are in
 Section 6.4.3 below.

6.4.2. Procedures for the PLR before Local Repair

 A PLR that determines to use facility-backup to protect a given LSP
 should select a bypass tunnel to use, taking into account whether
 node protection is to be provided, what bandwidth was requested,
 whether a bandwidth guarantee is desired, and what link attribute
 filters were specified in the FAST_REROUTE object.  The selection of
 a bypass tunnel for a protected LSP is performed by the PLR when the
 LSP is first set up.

Pan, et al. Standards Track [Page 24] RFC 4090 RSVP-TE Fast Reroute May 2005

6.4.3. Procedures for the PLR during Local Repair

 When the PLR detects a link or/and node failure condition, it has to
 reroute the data traffic onto the bypass tunnel and to start sending
 the control traffic for the protected LSP onto the bypass tunnel.
 The backup tunnel is identified by using the sender template-specific
 method.  The procedures to follow are similar to those described in
 Section 6.3.
  1. The SESSION is unchanged.
  1. The SESSION_ATTRIBUTE is unchanged except as follows: The

"Local protection desired", "Bandwidth protection desired", and

      "Node protection desired" flags SHOULD be cleared.  The "Label
      recording desired" MAY be modified.
  1. The IPv4 (or IPv6) tunnel sender address of the SENDER_TEMPLATE

is set to an address belonging to the PLR.

  1. The RSVP_HOP object MUST contain an IP source address belonging

to the PLR. Consequently, the MP will send messages back to the

      PLR with that IP address as the destination.
  1. The PLR MUST generate an EXPLICIT_ROUTE object toward the

egress. Detailed ERO processing is described below.

  1. The RRO object may have to be updated as described in Section

6.5.

 The PLR sends Path, PathTear, and ResvConf messages via the backup
 tunnel.  The MP sends Resv, ResvTear, and PathErr messages by sending
 them directly to the address in the RSVP_HOP object, as specified in
 [RSVP].
 If it is necessary to signal the backup prior to failure to determine
 the MP label to use, then the same Path message is sent.  In this
 case, the PLR SHOULD continue to send Path messages for the protected
 LSP along the normal route.  PathTear messages should be duplicated,
 with one sent along the normal route and one sent through the bypass
 tunnel.  The MP should duplicate the Resv and ResvTear messages and
 send them to both the PLR and the LSR indicated by the protected
 LSP's RSVP_HOP object.

Pan, et al. Standards Track [Page 25] RFC 4090 RSVP-TE Fast Reroute May 2005

6.4.4. Processing Backup Tunnel's ERO

 Procedures for ERO processing are described in [RSVP-TE].  This
 section describes additional ERO update procedures for Path messages
 that are sent over bypass tunnels.  If normal ERO processing rules
 were followed, the Merge Point would examine the first sub-object and
 likely reject it (Bad initial sub-object).  This is because the
 unmodified ERO might contain the IP address of a bypassed node (in
 the case of a NNHOP Bypass Tunnel) or of an interface that is
 currently down (in the case of a NHOP Backup Tunnel).  For this
 reason, the PLR invokes the following ERO procedures before sending a
 Path message via a bypass tunnel.
    Sub-objects belonging to abstract nodes that precede the Merge
    Point are removed, along with the first sub-object belonging to
    the MP.  A sub-object identifying the Backup Tunnel destination is
    then added.
    More specifically, the PLR MUST:
  1. remove all the sub-objects proceeding the first address

belonging to the MP, and

  1. replace this first MP address with an IP address of the MP.

(Note that this could be same address that was just removed.)

6.5. PLR Procedures during Local Repair

 In addition to the method-specific signaling and packet treatment,
 there is common signaling that should be followed.
 During fast reroute, for each protected LSP containing an RRO object,
 the PLR obtains the RRO from the protected LSP's stored RESV.  The
 PLR MUST update the IPv4 or IPv6 sub-object it inserted into the RRO
 by setting the "Local protection in use" and "Local Protection
 Available" flags.

6.5.1. Notification of Local Repair

 In many situations, the route used during local repair will be less
 than optimal.  The purpose of local repair is to keep high priority
 and loss-sensitive traffic flowing while a more optimal re-routing of
 the tunnel can be effected by the head-end of the tunnel.  Thus, the
 head-end has to know of the failure so that it may re-signal an
 optimal LSP.

Pan, et al. Standards Track [Page 26] RFC 4090 RSVP-TE Fast Reroute May 2005

 To provide this notification, the PLR SHOULD send a Path Error
 message with error code of "Notify" (Error code = 25) and an error
 value field of ss00 cccc cccc cccc, where ss=00 and the sub-code = 3
 ("Tunnel locally repaired") (see [RSVP-TE]).
 Additionally, a head-end may detect that an LSP has to be moved to a
 more optimal path by noticing failures reported via the IGP.  Note
 that in the case of inter-area TE LSP (TE LSP spanning areas), the
 head-end LSR will have to rely exclusively on Path Error messages to
 be informed of failures in another area.

6.5.2. Revertive Behavior

 Upon a failure event, a protected TE LSP is locally repaired by the
 PLR.  There are two basic strategies for restoring the TE LSP to a
 full working path.
  1. Global revertive mode: The head-end LSR of each tunnel is

responsible for reoptimizing the TE LSPs that used the failed

    resource.  There are several potential reoptimization triggers:
    RSVP error messages, inspection of OSPF LSAs or ISIS LSPs, and
    timers.  Note that this re-optimization process may proceed as
    soon as the failure is detected.  It is not tied to the
    restoration of the failed resource.
  1. Local revertive mode: Upon detecting that the resource is

restored, the PLR re-signals each of the TE LSPs that used to be

    routed over the restored resource.  Every TE LSP successfully
    re-signaled along the restored resource is switched back.
 There are several circumstances in which a local revertive mode might
 not be desirable.  In the case of resource flapping (not an uncommon
 failure type), this could generate multiple traffic disruptions.
 Therefore, in the local revertive mode, the PLR should implement a
 means to dampen the re-signaling process in order to limit potential
 disruptions due to flapping.
 In the local revertive mode, any TE LSP will be switched back,
 without any distinction, whereas in the global revertive mode, the
 decision to reuse the restored resource is made by the head-end LSR
 based on the TE LSP attributes.  When the head-end learns of the
 failure, it may reoptimize the protected LSP tunnel along a different
 and more optimal path, as it has a more complete view of the
 resources and TE LSP constraints.  This means that the old LSP that
 has been reverted to may no longer be optimal.  Note that in the case
 of inter-area LSP, where the TE LSP path computation might be done on
 some Path Computation Element, the reoptimization process can

Pan, et al. Standards Track [Page 27] RFC 4090 RSVP-TE Fast Reroute May 2005

 still be triggered on the Head-End LSP.  The local revertive mode
 is optional.
 However, there are circumstances in which the head-end does not have
 the ability to reroute the TE LSP (e.g., if the protected LSP is
 pinned down, as may be desirable if the paths are determined by using
 an off-line optimization tool), or if the head-end does not have the
 complete TE topology information (depending on the path computation
 scenario).  In those cases, the local revertive mode might be an
 interesting option.
 The globally revertive mode SHOULD always be used.  Note that a link
 or node "failure" may be due to the facility being permanently taken
 out of service.  Local revertive mode is optional.  When used in
 combination, the global mode may rely solely on timers to do the
 reoptimization.  When local revertive mode is not used, head-end LSRs
 SHOULD react to RSVP error messages and/or IGP indications in order
 to make a timely response.
 Interoperability: If a PLR is configured with the local revertive
 mode but the MP is not, any attempt from the PLR to resignal the TE
 LSP over the restored resource will fail, as the MP will not send any
 Resv message.  The PLR will still refresh the TE LSP over the backup
 tunnel.  The TE LSP will not revert to the restored resource;
 instead, it will continue to use the backup until it is re-optimized.

7. Merge Node Behavior

 An LSR is a Merge Point if it receives the Path message for a
 protected LSP and one or more messages for a backup LSP that is
 merged into that protected LSP.  In the one-to-one backup method, the
 LSR is aware that it is a merge node prior to failure.  In the
 facility backup method, the LSR may not know that it is a Merge Point
 until a failure occurs and it receives a backup LSP's Path message.
 Therefore, an LSR that is on the path of a protected LSP SHOULD
 always assume that it is a merge point.
 When a MP receives a backup LSP's Path message through a bypass
 tunnel, the Send_TTL in the Common Header may not match the TTL of
 the IP packet within which the Path message was transported.  This is
 expected behavior.

7.1. Handling Backup Path Messages before Failure

 There are two circumstances in which a Merge Point will receive Path
 messages for a backup path prior to failure.  In the first case, if a
 PLR is providing local protection via the one-to-one backup method,
 the detour will be signaled and must be properly handled by the MP.

Pan, et al. Standards Track [Page 28] RFC 4090 RSVP-TE Fast Reroute May 2005

 In this case, the backup LSP may be signaled via the sender
 template-specific method or via the path-specific method.
 In the second case, if the Merge Point does not provide labels global
 to the MP and record them in a Label sub-object of the RRO, or if the
 PLR does not use such recorded information, the PLR may signal the
 backup path as described in Section 6.4.1.  This will determine the
 label to use if the PLR is providing protection according to the
 facility backup method.  In this case, the backup LSP is signaled via
 the sender template-specific method.
 The reception of a backup LSP's path message does not indicate that a
 failure has occurred or that the incoming protected LSP will no
 longer be used.

7.1.1. Merging Backup Paths using the Sender Template-Specific Method

 An LSR may receive multiple Path messages for one or more backup LSPs
 and, possibly, for the protected LSP.  Each of these Path messages
 will have a different SENDER_TEMPLATE.  The protected LSP can be
 recognized because it will include the FAST_REROUTE object or have
 the "local protection desired" flag set in the SESSION_ATTRIBUTE
 object, or both.
 If the outgoing interface and next-hop LSR are the same, then the
 Path messages are eligible for merging.  Similarly to the
 specification in [RSVP-TE] for merging of RESV messages, only Path
 messages whose ERO from that LSR to the egress is the same can be
 merged.  If merging occurs and one of the Path messages merged was
 for the protected LSP, then the final Path message to be sent MUST be
 that of the protected LSP.  This merges the backup LSPs into the
 protected LSP at that LSR.  Once the final Path message has been
 identified, the MP MUST start to refresh it downstream periodically.
 If merging occurs and all the Path messages were for backup LSPs,
 then the DETOUR object, if any, should be altered as specified in
 Section 8.1

7.1.2. Merging Detours using the Path-Specific Method

 An LSR (that is, an MP) may receive multiple Path messages from
 different interfaces with identical SESSION and SENDER_TEMPLATE
 objects.  In this case, Path state merging is REQUIRED.  The merging
 rule is as follows:
 If all Path messages have neither a FAST_REROUTE nor a DETOUR object,
 or if the MP is the egress of the LSP, no merging is required.  The
 messages are processed according to [RSVP-TE].

Pan, et al. Standards Track [Page 29] RFC 4090 RSVP-TE Fast Reroute May 2005

 Otherwise, the MP MUST record the Path state and the incoming
 interface.  If the Path messages do not share an outgoing interface
 and a next-hop LSR, the MP MUST consider them to be independent LSPs
 and MUST NOT merge them.
 For all the Path messages that share the same outgoing interface and
 next-hop LSR, the MP runs the following procedure to create a Path
 message to forward downstream.
   1. If one or more of the Path messages is for the protected LSP (a
      protected LSP is one originated from this node, or with the
      FAST_REROUTE object, or without the DETOUR object), one of these
      must become the chosen Path message.  There could be more than
      one; in that case, which one to forward is a local decision.
      Quit.
   2. From the remaining set of Detour Path messages, eliminate from
      consideration those that traverse nodes that others want to
      avoid.
   3. If several still remain, which one to forward is a local
      decision.  If none remain, then the MP MAY try to find a new
      route that avoids all nodes that merging Detour Paths want to
      avoid; it will forward a Path message with that ERO.
 Once the final Path message has been identified, the MP MUST start to
 refresh it downstream periodically.  Other LSPs are considered merged
 at this node.  For bandwidth reservations on the outgoing link, any
 merging should be considered to have occurred before bandwidth is
 reserved.  Thus, even though Fixed Filter style is specified,
 multiple detours and/or their protected LSP (which are to be merged
 due to sharing an outgoing interface and next-hop LSR) will reserve
 only the bandwidth of the final Path message on that outgoing
 interface.
 If no merged Path message can be constructed, the MP SHOULD send a
 PathErr in response to the most recently received detour Path
 message.  If a protected Path is chosen to be forwarded but it
 traverses nodes that some detours want to avoid, PathErrs SHOULD be
 sent in response to those detour Paths which cannot merge.

Pan, et al. Standards Track [Page 30] RFC 4090 RSVP-TE Fast Reroute May 2005

7.1.2.1. An Example of Path Message Merging

              R7---R8---R9-\
              |    |    |   \
         R1---R2---R3---R4---R5---R6
         Protected LSP:  [R1->R2->R3->R4->R5->R6]
         R2's Detour:    [R2->R7->R8->R9->R4->R5->R6]
         R3's Detour:    [R3->R8->R9->R5->R6]
         Example 4.  Path Message Merging
 In Example 4, R8 will receive Path messages that have the same
 SESSION and SENDER_TEMPLATE from detours for R2 and R3.  During
 merging at R8, because detour R3 has a shorter ERO path length (that
 is, ERO is [R9->R5->R6], and path length is 3), R8 will select it as
 the final LSP and will only propagate its Path messages downstream.
 Upon receiving a Resv (or a ResvTear) message, R8 must relay the
 messages toward both R2 and R3.
 R5 has to merge as well, and it will select the main LSP, since it
 has the FAST_REROUTE object.  Thus, the detour LSP terminates at R5.

7.1.3. Message Handling for Merged Detours

 When an LSR receives a ResvTear for an LSP, the LSR must determine
 whether it has an alternate associated LSP.  For instance, if the
 ResvTear was received for a protected LSP but an associated backup
 LSP has not received a ResvTear, then the LSR has an alternate
 associated LSP.  If the LSR does not have an alternate associated
 LSP, then the MP MUST propagate the ResvTear toward the LSP's
 ingress, and, for each backup LSP merged into that LSP at this LSR,
 the ResvTear SHOULD also be propagated along the backup LSP.
 The MP may receive PathTear messages for some of the merging LSPs.
 PathTear messages SHOULD NOT be propagated downstream until the MP
 has received PathTear messages for each of the merged LSPs.  However,
 the fact that one or more of the merged LSPs has been torn down
 should be reflected in the downstream message, such as by changing
 the DETOUR object, if there is one.

7.2. Handling Failures

 When a downstream LSR detects a local link failure, for any protected
 LSPs routed over the failed link, Path and Resv state MUST NOT be
 cleared, and PathTear and ResvErr messages MUST NOT be sent
 immediately.  If this is not the case, then the facility backup
 method will not work.  Furthermore, a downstream LSR SHOULD reset the

Pan, et al. Standards Track [Page 31] RFC 4090 RSVP-TE Fast Reroute May 2005

 refresh timers for these LSPs as if they had just been refreshed.
 This is to allow time for the PLR to begin refreshing state via the
 bypass tunnel.  State MUST be removed if it has not been refreshed
 before the refresh timer expires.  This allows the facility backup
 method to work without requiring that it signal backup paths through
 the bypass tunnel before failure.
 After a failure has occurred, the MP must still send Resv messages
 for the backup LSPs associated with the protected LSPs that have
 failed.  If the backup LSP was sent through a bypass tunnel, then the
 PHOP object in its Path message will have the IP address of the
 associated PLR.  This will ensure that Resv state is refreshed.
 Once the local link has recovered, the MP may or may not accept Path
 messages for existing protected LSPs that had failed over to their
 backup.

8. Behavior of All LSRs

 The objects and methods defined in this document require behavior
 from all LSRs in the traffic-engineered network, even if an LSR is
 not along the path of a protected LSP.
 First, if a DETOUR object is included in the backup LSP's path
 message for the sender template-specific method, the LSRs in the
 traffic-engineered network should support the DETOUR object.
 Second, if the path-specific method is to be supported for the one-
 to-one backup method, it is necessary that the LSRs in the traffic-
 engineered network be capable of merging detours as specified in
 Section 8.1.
 It is possible to avoid specific LSRs that do not support this
 behavior by assigning a link attribute to all the links of those LSPs
 and then requesting that backup paths exclude this link attribute.

8.1. Merging Detours in the Path-Specific Method

 If multiple Path Messages for different detours are received with the
 same SESSION, SENDER_TEMPLATE, outgoing interface, and next-hop LSR,
 then the LSR must function as a Detour Merge Point and merge the
 detour Path Messages.  This merging should occur as specified in
 Section 7.1.2 and shown in Example 4.
 In addition, it is necessary to update the DETOUR object to reflect
 the merging that has taken place.  This is done using the following
 algorithm to format the outgoing DETOUR object for the final LSP:

Pan, et al. Standards Track [Page 32] RFC 4090 RSVP-TE Fast Reroute May 2005

  1. Combine all the (PLR_ID, Avoid_Node_ID) pairs from all the DETOUR

objects of all merged LSPs into a new object. Ordering is

     insignificant.

9. Security Considerations

 This document does not introduce new security issues.  The security
 considerations pertaining to the original RSVP protocol [RSVP] remain
 relevant.
 Note that the facility backup method requires that a PLR and its
 selected merge point trust RSVP messages received from each other.

10. IANA Considerations

 IANA [RFC-IANA] has assigned the following RSVP Class Numbers for
 objects defined in this document.

10.1. DETOUR Object

 IANA has assigned:
    63  DETOUR
        Class Types or C-Types:
           7  IPv4
           8  IPv6
 Future C-Types will be assigned using the following guidelines:
     C-Types 0 through 127 are assigned by Standards Action.
     C-Types 128 through 191 are assigned by Expert Review.
     C-Types 192 through 255 are reserved for Vendor Private Use.
 For C-Types in the range 192 through 255, the first four octets of
 the DETOUR object after the C-Type must be the Vendor's SMI Network
 Management Private Enterprise Code (see [ENT]) in network byte order.

Pan, et al. Standards Track [Page 33] RFC 4090 RSVP-TE Fast Reroute May 2005

10.2. FAST_REROUTE Object

 IANA has assigned:
    205  FAST_REROUTE
         Class Types or C-Types:
           1   FAST_REROUTE Type 1
           7   RESERVED
 In the FAST_REROUTE object, C-Type 7 is reserved as it is still used
 by pre-standard implementations.  Future C-Types will be assigned
 using the following guidelines:
     C-Types 0 through 127 are assigned by Standards Action.
     C-Types 128 through 191 are assigned by Expert Review.
     C-Types 192 through 255 are reserved for Vendor Private Use.
 For C-Types in the range 192 through 255, the first four octets of
 the FAST_REROUTE object after the C-Type must be the Vendor's SMI
 Network Management Private Enterprise Code (see [ENT]) in network
 byte order.

Pan, et al. Standards Track [Page 34] RFC 4090 RSVP-TE Fast Reroute May 2005

11. Contributors

 This document was written by George Swallow, Ping Pan, Alia Atlas,
 Jean Philippe Vasseur, Markus Jork, Der-Hwa Gan, and Dave Cooper.
 Jean Philippe Vasseur
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA 01719
 USA
 Phone:  +1 978 497 6238
 EMail: jpv@cisco.com
 Markus Jork
 Quarry Technologies
 8 New England Executive Park
 Burlington, MA 01803
 USA
 Phone: +1 781 359 5071
 EMail: mjork@quarrytech.com
 Der-Hwa Gan
 Juniper Networks
 1194 N.Mathilda Ave
 Sunnyvale, CA 94089
 USA
 Phone: +1 408 745 2074
 EMail: dhg@juniper.net
 Dave Cooper
 Global Crossing
 960 Hamlin Court
 Sunnyvale, CA 94089
 USA
 Phone: +1 916 415 0437
 EMail: dcooper@gblx.net

Pan, et al. Standards Track [Page 35] RFC 4090 RSVP-TE Fast Reroute May 2005

12. Acknowledgments

 We would like to acknowledge input and helpful comments from Rob
 Goguen, Tony Li, Yakov Rekhter and Curtis Villamizar.  Especially, we
 thank those, who have been involved in interoperability testing and
 field trails, and provided invaluable ideas and suggestions.  They
 are Rob Goguen, Carol Iturralde, Brook Bailey, Safaa Hasan, Richard
 Southern, and Bijan Jabbari.

13. Normative References

 [RSVP]       Braden, R., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
              1 Functional Specification", RFC 2205, September 1997.
 [RSVP-TE]    Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
              V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.
 [RFC-WORDS]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC-IANA]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.
 [ENT]        IANA PRIVATE ENTERPRISE NUMBERS,
              http://www.iana.org/assignments/enterprise-numbers

Pan, et al. Standards Track [Page 36] RFC 4090 RSVP-TE Fast Reroute May 2005

Authors' Addresses

 George Swallow
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA 01719
 USA
 Phone:  +1 978 244 8143
 EMail:  swallow@cisco.com
 Ping Pan
 Hammerhead Systems
 640 Clyde Court
 Mountain View, CA 94043
 USA
 EMail: ppan@hammerheadsystems.com
 Alia Atlas
 Avici Systems
 101 Billerica Avenue
 N. Billerica, MA 01862
 USA
 Phone: +1 978 964 2070
 EMail: aatlas@avici.com

Pan, et al. Standards Track [Page 37] RFC 4090 RSVP-TE Fast Reroute May 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at ietf-
 ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Pan, et al. Standards Track [Page 38]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4090.txt · Last modified: 2005/05/25 18:05 (external edit)