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Versions: (draft-ayyangar-ccamp-lsp-stitching) 00 01 02 03 04 05 06 RFC 5150

Network Working Group                                   A. Ayyangar, Ed.
Internet-Draft                                          Juniper Networks
Expires: March 26, 2006                                      JP. Vasseur
                                                     Cisco Systems, Inc.
                                                      September 22, 2005


Label Switched Path Stitching with Generalized MPLS Traffic Engineering
                 draft-ietf-ccamp-lsp-stitching-02.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   In certain scenarios, there may be a need to combine together
   different Generalized Multi-Protocol Label Switching (GMPLS) Label
   Switched Paths (LSPs) such that in the data plane, a single end-to-
   end (e2e) LSP is realized and all traffic from one LSP is switched
   onto the other LSP.  We will refer to this as "LSP stitching".  This
   document covers cases where: a) the node performing the stitching
   does not require configuration of every LSP pair to be stitched



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   together b) the node performing the stitching is not the egress of
   any of the LSPs c) LSP stitching not only results in an end-to-end
   LSP in the data plane, but there is also a corresponding end-to-end
   LSP (RSVP session) in the control plane.

   It may be possible to configure a GMPLS node to switch the traffic
   from an LSP for which it is the egress, to another LSP for which it
   is the ingress, without requiring any signaling or routing extensions
   whatsoever, completely transparent to other nodes.  This will also
   result in LSP stitching in the data plane.  However, this document
   does not cover this scenario of LSP stitching.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Conventions used in this document  . . . . . . . . . . . .  3
   2.  Comparison with LSP Hierarchy  . . . . . . . . . . . . . . . .  4
   3.  Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1   Triggers for LSP segment setup . . . . . . . . . . . . . .  5
     3.2   Applications . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Routing aspects  . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Signaling aspects  . . . . . . . . . . . . . . . . . . . . . .  7
     5.1   RSVP-TE signaling extensions . . . . . . . . . . . . . . .  7
       5.1.1   Creating and preparing LSP segment for stitching . . .  7
       5.1.2   Stitching the e2e LSP to the LSP segment . . . . . . .  9
       5.1.3   RRO Processing for e2e LSP . . . . . . . . . . . . . . 10
       5.1.4   Teardown of LSP segment  . . . . . . . . . . . . . . . 11
       5.1.5   Teardown of e2e LSP  . . . . . . . . . . . . . . . . . 11
     5.2   Summary of LSP Stitching procedures  . . . . . . . . . . . 12
       5.2.1   Example topology . . . . . . . . . . . . . . . . . . . 12
       5.2.2   LSP segment setup  . . . . . . . . . . . . . . . . . . 12
       5.2.3   Setup of e2e LSP . . . . . . . . . . . . . . . . . . . 13
       5.2.4   Stitching of e2e LSP into an LSP segment . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
     7.1   Attribute Flags for LSP_ATTRIBUTES object  . . . . . . . . 15
     7.2   New Error Codes  . . . . . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1   Normative References . . . . . . . . . . . . . . . . . . . 17
     9.2   Informative References . . . . . . . . . . . . . . . . . . 17
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18
       Intellectual Property and Copyright Statements . . . . . . . . 19








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1.  Introduction

   This document describes the mechanisms to accomplish LSP stitching in
   the scenarios described above.

   LSP hierarchy ([2]) provides signaling and routing procedures so
   that:

   a.  A Hierarchical LSP (H-LSP) can be created.  Such an LSP created
       in one layer can provide a data link to LSPs in higher layers.
       Also one or more LSPs can be nested into this H-LSP.

   b.  An H-LSP may be managed and advertised (although this is not a
       requirement) as a Traffic Engineering (TE) link.  Advertising an
       H-LSP as a TE link allows other nodes in the TE domain in which
       it is advertised to use this H-LSP in path computation.  If the
       H-LSP TE link is advertised in the same instance of control plane
       (TE domain) in which the H-LSP was provisioned, it is then
       defined as a forwarding adjacency LSP (FA-LSP) and GMPLS nodes
       can form a forwarding adjacency (FA) over this FA-LSP.  There is
       usually no routing adjacency between end points of an FA.  An
       H-LSP may also be advertised as a TE link in a different TE
       domain.  In this case, the end points of the H-LSP are required
       have a routing adjacency between them.

   c.  RSVP signaling for LSP setup can occur between nodes that do not
       have a routing adjacency.

   A stitched TE LSP comprises of different LSP segments (S-LSPs) that
   are connected together in the data plane in such a way that a single
   end-to-end LSP is realized in the data plane.  In this document, we
   define the concept of LSP stitching and detail the control plane
   mechanisms and procedures to accomplish this.  Where applicable,
   similarities and differences between LSP hierarchy and LSP stitching
   are highlighted.  Signaling extensions required for LSP stitching are
   also described here.

1.1  Conventions used in this document

   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 RFC 2119 [1].









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2.  Comparison with LSP Hierarchy

   In case of LSP stitching, instead of an H-LSP, an "LSP segment"
   (S-LSP) is created between two GMPLS nodes.  An S-LSP for stitching
   is considered to be the moral equivalent of an H-LSP for nesting.  An
   S-LSP created in one layer, unlike an H-LSP, provides a data link to
   other LSPs in the same layer.  Similar to an H-LSP, an S-LSP could be
   managed and advertised, although it is not required, as a TE link,
   either in the same TE domain as it was provisioned or a different
   one.  If advertised, other GMPLS nodes could used the corresponding
   S-LSP TE link in path computation.  While there is a forwarding
   adjacency between end points of an H-LSP TE link, there is no
   forwarding adjacency between end points of an S-LSP TE link.  In this
   aspect, an H-LSP TE link more closely resembles a 'basic' TE link as
   compared to an S-LSP TE link.

   While LSP hierarchy allows more than one LSP to be mapped to an
   H-LSP, in case of LSP stitching, at most one LSP may be associated
   with an S-LSP.  E.g. if LSP-AB is an H-LSP between nodes A and B,
   then multiple LSPs, say LSP1, LSP2, LSP3 could potentially be 'nested
   into' LSP-AB.  This is achieved by exchanging a unique label for each
   of LSP1..3 over the LSP-AB hop thereby permitting LSP1..3 to share
   the H-LSP LSP-AB.  Each of LSP1..3 may reserve some bandwidth on
   LSP-AB.  On the other hand, if LSP-AB is an S-LSP, then at most one
   LSP, say LSP1 may be stitched to the S-LSP LSP-AB.  LSP-AB is
   dedicated to LSP1 and no other LSPs can be associated with LSP-AB.
   The entire bandwith on S-LSP LSP-AB is allocated to LSP1.  However,
   several S-LSPs MAY be bundled into a TE link ([11]), similar to
   H-LSPs.

   The LSPs LSP1..3 which are either nested or stitched into another LSP
   are termed as end-to-end (e2e) LSPs in the rest of this document.
   Routing procedures specific to LSP stitching are detailed in
   Section 4.

   Targetted (non-adjacent nodes) RSVP signaling defined in [2] is
   required for LSP stitching of an e2e LSP to an S-LSP.  Specific
   extensions for LSP stitching are described later in Section 5.1.
   Therefore, in the control plane, there is one RSVP session
   corresponding to the e2e LSP as well as one for each S-LSP.  The
   creation and termination of an S-LSP may be dictated by
   administrative control (statically provisioned) or due to another
   incoming LSP request (dynamic).  Triggers for dynamic creation of an
   S-LSP may be different from that of an H-LSP and will be described in
   detail later.






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3.  Usage

3.1  Triggers for LSP segment setup

   An S-LSP may be created either by administrative control
   (configuration trigger) or dynamically due to an incoming LSP
   request.  LSP Hierarchy ([2]) defines one possible trigger for
   dynamic creation of FA-LSP by introducing the notion of LSP regions
   based on Interface Switching Capabilities.  As per [2], dynamic FA-
   LSP creation may be triggered on a node when an incoming LSP request
   crosses region boundaries.  However, this trigger MUST NOT be used
   for creation of S-LSP for LSP stitching as described in this
   document.  In case of LSP stitching, the switching capabilities of
   the previous hop and the next hop TE links MUST be the same.
   Therefore, local policies configured on the node SHOULD be used for
   dynamic creation of LSP segments.

   Other possible triggers for dynamic creation of both H-LSPs and
   S-LSPs include cases where an e2e LSP may cross domain boundaries or
   satisfy locally configured policies on the node as described in [8].

3.2  Applications

   LSP stitching procedures described in this document are applicable to
   GMPLS nodes that need to associate an e2e LSP with another S-LSP of
   the same switching type and LSP hierarchy procedures do not apply.
   E.g. if an e2e lambda LSP traverses an LSP segment TE link which is
   also lambda switch capable, then in this case LSP hierarchy is not
   possible.

   LSP stitching procedures could be used for inter-domain TE LSP
   signaling to stitch an inter-domain LSP to a local intra-domain TE
   S-LSP ([8]).

   LSP stitching could also be useful in networks to bypass legacy nodes
   which may not have certain new capabilities in the control plane
   and/or data plane.  E.g. one suggested usage in case of P2MP RSVP
   LSPs ([7]) is the use of LSP stitching to stitch a P2MP RSVP LSP to
   an LSP segment between P2MP capable LSRs in the network.  The LSP
   segment would traverse legacy LSRs that may be incapable of acting as
   P2MP branch points, thereby shielding them from the P2MP control and
   data path.  Note, however, that such configuration may limit the
   attractiveness of RSVP P2MP and should carefully be examined before
   deployment.







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4.  Routing aspects

   An S-LSP is created between two GMPLS nodes and it may traverse zero
   or more GMPLS nodes.  There is no forwarding adjacency between the
   end points of an S-LSP TE link.  So, although in the TE topology, the
   end points of an S-LSP TE link are adjacent, in the data plane, these
   nodes do not have an adjacency.  Hence any data plane resource
   identifier between these nodes is also meaningless.  The traffic that
   arrives at the head end of the S-LSP is switched into the S-LSP
   contiguously with a label swap and no label is associated directly
   between the end nodes of the S-LSP itself.

   An S-LSP MAY be treated and managed as a TE link.  This TE link MAY
   be numbered or unnumbered.  For an unnumbered S-LSP TE link, the
   schemes for assignment and handling of the local and remote link
   identifiers as specified in [10] SHOULD be used.  ISIS/OSPF may flood
   the TE information associated with an S-LSP TE link, when
   appropriate.  Mechanisms similar to that for regular (basic) TE links
   SHOULD be used to flood S-LSP TE links.  Advertising or flooding the
   S-LSP TE link is not a requirement for LSP stitching.  Discretion
   should be used when advertising an S-LSP TE link in an IGP.  If
   advertised, this TE information will exist in the TE database (TED)
   and can then be used for path computation by other GMPLS nodes in the
   TE domain in which it is advertised.

   If an S-LSP is advertised as a TE link in the same TE domain in which
   it was provisioned, there is no need for a routing adjacency between
   end points of this S-LSP TE link.  If an S-LSP TE link is advertised
   in a different TE domain, the end points of that TE link SHOULD have
   a routing adjacency between them.

   The TE parameters defined for an FA in [2] SHOULD be used for an
   S-LSP TE link as well.  The switching capability of an S-LSP TE link
   MUST be equal to the switching type of the underlying S-LSP; i.e. an
   S-LSP TE link provides a data link to other LSPs in the same layer,
   so no hierarchy is possible.

   An S-LSP MUST NOT admit more than one e2e LSP into it.  However,
   multiple S-LSPs between the same pair of nodes MAY be bundled using
   the concept of Link Bundling ([11]) into a single TE link.  So, while
   an S-LSP can have exactly one e2e LSP associated with it, a bundled
   TE link comprising of multiple S-LSPs, MAY admit more than one e2e
   LSP.  When any component S-LSP is allocated for an e2e LSP, the
   component's unreserved bandwidth SHOULD be set to zero and the
   Minimum and Maximum LSP bandwidth of the TE link SHOULD be
   recalculated.  This will prevent more than one LSP from being
   computed and admitted over an S-LSP.




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5.  Signaling aspects

   The end nodes of an S-LSP may or may not have a routing adjacency.
   However, they SHOULD have a signaling adjacency (RSVP neighbor
   relationship) and will exchange RSVP messages with each other.  It
   may, in fact, be desirable to exchange RSVP Hellos directly between
   the LSP segment end points to allow support for state recovery during
   Graceful Restart procedures as described in [4].

   In order to signal an e2e LSP over an LSP segment, signaling
   procedures described in section 8.1.1 of [2] MUST be used.
   Additional signaling extensions for stitching are described in the
   next section.

5.1  RSVP-TE signaling extensions

   The signaling extensions described here MUST be used for stitching an
   e2e packet or non-packet GMPLS LSP ([4]), to an S-LSP.

   Stitching an e2e LSP to an LSP segment involves the following two
   step process:

   a.  Creating and preparing the S-LSP for stitching by signaling the
       desire to stitch between end points of the S-LSP and

   b.  Stitching the e2e LSP to the S-LSP


5.1.1  Creating and preparing LSP segment for stitching

   If a GMPLS node desires to perform LSP stitching, then it MUST
   indicate this in the Path message for the S-LSP that it plans to use
   for stitching.  This signaling explicitly informs the S-LSP egress
   node that the ingress node is planning to perform stitching over the
   S-LSP.  Since an S-LSP is not conceptually different from any other
   LSP, explicitly signaling 'LSP stitching desired' helps clarify the
   data plane actions to be carried out when the S-LSP is used by some
   other e2e LSP.  Also, in case of packet LSPs, this is what allows the
   egress of the S-LSP to carry out label allocation as explained below.
   Also, so that the head-end node can ensure that correct stitching
   actions will be carried out at the egress node, the egress node MUST
   signal this information back to the head-end node in the Resv, as
   explained below.

   In order to request LSP stitching on the S-LSP, we define a new bit
   in the Attributes Flags TLV of the LSP_ATTRIBUTES object defined in
   [3]:




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   Bit Number 5 (TBD): LSP stitching desired bit - This bit SHOULD be
   set in the Attributes Flags TLV of the LSP_ATTRIBUTES object in the
   Path message for the S-LSP by the head-end of the S-LSP, that desires
   LSP stitching.  This bit MUST NOT be modified by any other nodes in
   the network.  Nodes other than the egress of the S-LSP SHOULD ignore
   this bit.

   An LSP segment can be used for stitching only if the egress node of
   the S-LSP is also ready to participate in stitching.  In order to
   indicate this to the head-end node of the S-LSP, the following new
   bit is defined in the Flags field of the RRO Attributes subobject:
   Bit Number 5 (TBD): LSP segment stitching ready.

   If an egress node of the S-LSP receiving the Path message, supports
   the LSP_ATTRIBUTES object and the Attributes Flags TLV, and also
   recognizes the "LSP stitching desired" bit, but cannot support the
   requested stitching behavior, then it MUST send back a PathErr
   message with an error code of "Routing Problem" and an error sub-
   code="Stitching unsupported" (TBD) to the head-end node of the S-LSP.

   If an egress node receiving a Path message with the "LSP stitching
   desired" bit set in the Flags field of received LSP_ATTRIBUTES,
   recognizes the object, the TLV and the bit and also supports the
   desired stitching behavior, then it MUST allocate a non-NULL label
   for that S-LSP in the corresponding Resv message.  Also, so that the
   head-end node can ensure that the correct label (forwarding) actions
   will be carried out by the egress node and that the S-LSP can be used
   for stitching, the egress node MUST set the "LSP segment stitching
   ready" bit defined in the Flags field of the RRO Attribute sub-
   object.

   Finally, if the egress node for the S-LSP supports the LSP_ATTRIBUTES
   object but does not recognize the Attributes Flags TLV, or supports
   the TLV as well but does not recognize this particular bit, then it
   SHOULD simply ignore the above request.

   An ingress node requesting LSP stitching MUST examine the RRO
   Attributes sub-object Flags corresponding to the egress node for the
   S-LSP, to make sure that stitching actions are carried out at the
   egress node.  It MUST NOT use the S-LSP for stitching if the "LSP
   segment stitching ready" bit is cleared.

5.1.1.1  Steps to support Penultimate Hop Popping

   Note that this section is only applicable to packet LSPs that use
   Penultimate Hop Popping (PHP) at the last hop, where the egress node
   distributes the Implicit NULL Label ([9]) in the Resv Label.  These
   steps MUST NOT be used for a non-packet LSP and for packet LSPs where



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   PHP is not desired.

   When the egress node of an S-LSP receives a Path message for an e2e
   LSP using this S-LSP and this is a packet LSP, it SHOULD first check
   if it is also the egress for the e2e LSP.  If the egress node is the
   egress for both the S-LSP as well as the e2e TE LSP, and this is a
   packet LSP which requires PHP, then the node MUST send back a Resv
   trigger message for the S-LSP with a new label corresponding to the
   Implicit NULL label.  Note that this operation does not cause any
   traffic disruption since the S-LSP is not carrying any traffic at
   this time, since the e2e LSP has not yet been established.

5.1.2  Stitching the e2e LSP to the LSP segment

   When a GMPLS node receives an e2e LSP request, depending on the
   applicable trigger, it may either dynamically create an S-LSP based
   on procedures described above or it may map an e2e LSP to an existing
   S-LSP.  The switching type in the Generalized Label Request of the
   e2e LSP MUST be equal to the switching type of the S-LSP.  Other
   constraints like ERO, bandwidth, local TE policies MUST also be used
   for S-LSP selection or signaling.  In either case, once an S-LSP has
   been selected for an e2e LSP, the following procedures MUST be
   followed in order to stitch an e2e LSP to an S-LSP.

   The GMPLS node receiving the e2e LSP setup Path message MUST use the
   signaling procedures described in [2] to send the Path message to the
   end point of the S-LSP.  In this Path message, the node MUST identify
   the S-LSP in the RSVP_HOP.  An egress node receiving this RSVP_HOP
   should also be able to identify the S-LSP TE link based on the
   information signaled in the RSVP_HOP.  If the S-LSP TE link is
   numbered, then the addressing scheme as proposed in [2] SHOULD be
   used to number the S-LSP TE link.  If the S-LSP TE link is
   unnumbered, then any of the schemes proposed in [10] SHOULD be used
   to exchange S-LSP TE link identifiers between the S-LSP end points.
   If the TE link is bundled, the RSVP_HOP SHOULD identify the component
   link as defined in [11].

   In case of a bidirectional e2e TE LSP, an Upstream Label MUST be
   signaled in the Path message for the e2e LSP over the S-LSP hop.
   However, since there is no forwarding adjacency between the S-LSP end
   points, any label exchanged between them has no significance.  So the
   node MAY chose any label value for the Upstream Label.  The label
   value chosen and signaled by the node in the Upstream Label is out of
   the scope of this document and is specific to the implementation on
   that node.  The egress node receiving this Path message MUST ignore
   the Upstream Label in the Path message over the S-LSP hop.

   The egress node receiving this Path message MUST signal a Label in



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   the Resv message for the e2e TE LSP over the S-LSP hop.  Again, since
   there is no forwarding adjacency between the egress and ingress S-LSP
   nodes, any label exchanged between them is meaningless.  So, the
   egress node MAY choose any label value for the Label.  The label
   value chosen and signaled by the egress node is out of the scope of
   this document and is specific to the implementation on the egress
   node.  The egress S-LSP node SHOULD also carry out data plane
   operations so that traffic coming in on the S-LSP is switched over to
   the e2e LSP downstream, if the egress of the e2e LSP is some other
   node downstream.  If the e2e LSP is bidirectional, this means setting
   up label switching in both directions.  The Resv message from the
   egress S-LSP node is IP routed back to the previous hop (ingress of
   the S-LSP).  The ingress node stitching an e2e TE LSP to an S-LSP
   MUST ignore the Label object received in the Resv for the e2e TE LSP
   over the S-LSP hop.  The S-LSP ingress node SHOULD also carry out
   data plane operations so that traffic coming in on the e2e LSP is
   switched into the S-LSP.  It should also carry out actions to handle
   traffic in the opposite direction if the e2e LSP is bidirectional.

   Note that the label exchange procedure for LSP stitching on the S-LSP
   hop, is similar to that for LSP hierarchy over the H-LSP hop.  The
   difference is the lack of the significance of this label between the
   S-LSP end points in case of stitching.  Therefore, in case of
   stitching the recepients of the Label/Upstream Label MUST NOT process
   these labels.  Also, at most one e2e LSP is associated with one
   S-LSP.  If a node at the head-end of an S-LSP receives a Path Msg for
   an e2e LSP that identifies the S-LSP in the ERO and the S-LSP
   bandwidth has already been allocated to some other LSP, then regular
   rules of RSVP-TE pre-emption apply to resolve contention for S-LSP
   bandwidth.  If the LSP request over the S-LSP cannot be satisfied,
   then the node SHOULD send back a PathErr with the error codes as
   described in [5].

5.1.3  RRO Processing for e2e LSP

   RRO procedures for the S-LSP specific to LSP stitching are already
   described in Section 5.1.1.  In this section we will look at the RRO
   processing for the e2e LSP over the S-LSP hop.

   An e2e LSP traversing an S-LSP, SHOULD record in the RRO for that
   hop, an identifier corresponding to the S-LSP TE link.  This is
   applicable to both Path and Resv messages over the S-LSP hop.  If the
   S-LSP is numbered, then the IPv4 or IPv6 address subobject ([5])
   SHOULD be used to record the S-LSP TE link address.  If the S-LSP is
   unnumbered, then the Unnumbered Interface ID subobject as described
   in [10] SHOULD be used to record the node's Router ID and Interface
   ID of the S-LSP TE link.  In either case, the RRO subobject SHOULD
   identify the S-LSP TE link end point.  Intermediate links or nodes



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   traversed by the S-LSP itself SHOULD NOT be recorded in the RRO for
   the e2e LSP over the S-LSP hop.

5.1.4  Teardown of LSP segment

   S-LSP teardown follows the standard procedures defined in [5] and
   [4].  This includes procedures without and with setting the
   administrative status.  Teardown of S-LSP may be initiated by either
   the ingress, egress or any other node along the S-LSP path.
   Deletion/teardown of the S-LSP SHOULD be treated as a failure event
   for the e2e LSP associated with it and corresponding teardown or
   recovery procedures SHOULD be triggered for the e2e LSP.  In case of
   S-LSP teardown for maintenance purpose, the S-LSP ingress node MAY
   treat this to be equivalent to administratively shutting down a TE
   link along the e2e LSP path and take corresponding actions to notify
   the ingress of this event.  The actual signaling procedures to handle
   this event is out of the scope of this document.

5.1.5  Teardown of e2e LSP

   e2e LSP teardown also follows standard procedures defined in [5] and
   [4] either without or with the administrative status.  Note, however,
   that teardown procedures of e2e LSP and of S-LSP are independent of
   each other.  So, it is possible that while one LSP follows graceful
   teardown with adminstrative status, the other LSP is torn down
   without administrative status (using PathTear/ResvTear/PathErr with
   state removal).

   When an e2e LSP teardown is initiated from the head-end, and a
   PathTear arrives at the GMPLS stitching node, the PathTear message
   like the Path message MUST be IP routed to the LSP segment egress
   node with the destination IP address of the Path message set to the
   address of the S-LSP end node.  Router Alert MUST be off and RSVP TTL
   check MUST be disabled on the receiving node.  PathTear will result
   in deletion of RSVP states corresponding to the e2e LSP and freeing
   of label allocations and bandwidth reservations on the S-LSP.  The
   unreserved bandwidth on the S-LSP TE link SHOULD be re-adjusted.

   Similarly, a teardown of the e2e LSP may be initiated from the tail-
   end either using a ResvTear or a PathErr with state removal.  The
   egress of the S-LSP MUST propagate the ResvTear/PathErr upstream, IP
   routed to the ingress of the LSP segment.

   Graceful LSP teardown using ADMIN_STATUS as described in [4] is also
   applicable to stitched LSPs.

   If the S-LSP was statically provisioned, tearing down of an e2e LSP
   MAY not result in tearing down of the S-LSP.  If, however, the S-LSP



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   was dynamically setup due to the e2e LSP setup request, then
   depending on local policy, the S-LSP MAY be torn down if no e2e LSP
   is utilizing the S-LSP.  Although the S-LSP may be torn down while
   the e2e LSP is being torn down, it is RECOMMENDED that a delay be
   introduced in tearing down the S-LSP once the e2e LSP teardown is
   complete, in order to reduce the simultaneous generation of RSVP
   errors and teardown messages due to multiple events.  The delay
   interval may be set based on local implementation.  The RECOMMENDED
   interval is 30 seconds.

5.2  Summary of LSP Stitching procedures

5.2.1  Example topology

   The following topology will be used for the purpose of examples
   quoted in the following sections.


                     e2e LSP
      ++++++++++++++++++++++++++++++++++> (LSP1-2)

                LSP segment (S-LSP)
             =====================> (LSP-AB)
                  C --- E --- G
                 /|\    |   / |\
                / | \   |  /  | \
      R1 ---- A \ |  \  | /   | / B --- R2
                 \|   \ |/    |/
                  D --- F --- H

                      PATH
             ======================> (LSP stitching desired)
                      RESV
             <====================== (LSP segment stitching ready)

                      PATH (Upstream Label)
             +++++++++++++++++++++++
       ++++++                       +++++>
       <++++++                       ++++++
             +++++++++++++++++++++++
                      RESV (Label)



5.2.2  LSP segment setup

   Let us consider an S-LSP LSP-AB being setup between two nodes A and B
   which are more than one hop away.  Node A sends a Path message for



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   the LSP-AB with "LSP stitching desired" set in Flags field of
   LSP_ATTRIBUTES object.  If the egress node B is ready to carry out
   stitching procedures, then B will respond with "LSP segment stitching
   ready" set in the Flags field of the RRO Attributes subobject, in the
   RRO sent in the Resv for the S-LSP.  Once A receives the Resv for
   LSP-AB and sees this bit set in the RRO, it can then use LSP-AB for
   stitching.  A cannot use LSP-AB for stitching if the bit is cleared
   in the RRO.

5.2.3  Setup of e2e LSP

   Let us consider an e2e LSP LSP1-2 starting one hop before A on R1 and
   ending on node R2, as shown above.  If the S-LSP has been adevrtised
   as a TE link in the TE domain, and R1 and A are in the same domain,
   then R1 may compute a path for LSP1-2 over the S-LSP LSP-AB and
   identify the LSP-AB hop in the ERO.  If not, R1 may compute hops
   between A and B and A may use these ERO hops for S-LSP selection or
   signaling a new S-LSP.  Also, an S-LSP TE link cannot be
   distinguished from any basic TE link on R1.  If R1 and A are in
   different domains, then LSP1-2 is an inter-domain LSP.  In this case,
   S-LSP LSP-AB, similar to any other basic TE link in the domain will
   not be advertised outside the domain.  R1 would use either per-domain
   path computation ([12]) or PCE based computation ([13]) for LSP1-2.

5.2.4  Stitching of e2e LSP into an LSP segment

   When the Path message for the e2e LSP LSP1-2 arrives at node A, A
   matches the switching type of LSP1-2 with the S-LSP LSP-AB.  If the
   switching types are not equal, then LSP-AB cannot be used to stitch
   LSP1-2.  Once S-LSP LSP-AB to stitch LSP1-2 to has been determined
   successfully, the Path message for LSP1-2 is IP routed to node B with
   the IF_ID RSVP_HOP identifying the S-LSP LSP-AB.  When B receives
   this Path message for LSP1-2, if B is also the egress for LSP1-2, and
   if this is a packet LSP requiring PHP, then B will send a Resv
   refresh for LSP-AB with the NULL Label.  In this case, since B is not
   the egress, the Path message for LSP1-2 is propagated to R2.  The
   Resv for LSP1-2 from B is IP routed back to A with a Label value
   chosen by B. B also sets up its data plane to swap the Label sent to
   either G or H on the S-LSP with the Label received from R2.  Node A
   ignores the Label on receipt of the  Resv message and then propagates
   the Resv to R1.  A also sets up its data plane to swap the Label sent
   to R1 with the Label received on the S-LSP from C or D. This stitches
   the e2e LSP LSP1-2 to an S-LSP LSP-AB between nodes A and B. In the
   data plane, this yields a series of label swaps from R1 to R2 along
   e2e LSP LSP1-2.






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6.  Security Considerations

   Similar to [2], this document permits that the control interface over
   which RSVP messages are sent or received need not be the same as the
   data interface which the message identifies for switching traffic.
   Also, the 'sending interface' and 'receiving interface' may change as
   routing changes.  So, these cannot be used to establish security
   association between neighbors.  Mechanisms described in [6] should be
   re-examined and may need to be altered to define new security
   associations based on receiver's IP address instead of the sending
   and receiving interfaces.  Also, this document allows the IP
   destination address of Path and PathTear messages to be the IP
   address of a nexthop node (receiver's address) instead of the RSVP
   session destination address.  So, [6] should be revisited to check if
   IPSec AH is now a viable means of securing RSVP-TE messages.




































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7.  IANA Considerations

   The following values have to be defined by IANA for this document.
   The registry is http://www.iana.org/assignments/rsvp-parameters.

7.1  Attribute Flags for LSP_ATTRIBUTES object

   The following new bit is being defined for the Attributes Flags TLV
   in the LSP_ATTRIBUTES object.  The numeric value should be assigned
   by IANA.

   LSP stitching desired bit - Bit Number 5 (Suggested value)

   This bit is only to be used in the Attributes Flags TLV on a Path
   message.

   The 'LSP stitching desired bit' has a corresponding 'LSP segment
   stitching ready' bit (Bit Number 5) to be used in the RRO Attributes
   sub-object.

7.2  New Error Codes

   The following new error sub-code is being defined under the RSVP
   error-code "Routing Problem" (24).  The numeric error sub-code value
   should be assigned by IANA.

   Stitching unsupported - sub-code 23 (Suggested value)

   This error code is to be used only in an RSVP PathErr.






















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8.  Acknowledgments

   The authors would like to thank Adrian Farrel and Kireeti Kompella
   for their comments and suggestions.  The authors would also like to
   thank Dimitri Papadimitriou and Igor Bryskin for their thorough
   review of the document and discussions regarding the same.













































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9.  References

9.1  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Kompella, K. and Y. Rekhter, "LSP Hierarchy with Generalized
        MPLS TE", draft-ietf-mpls-lsp-hierarchy-08 (work in progress),
        September 2002.

   [3]  Farrel, A., "Encoding of Attributes for Multiprotocol Label
        Switching (MPLS) Label  Switched Path (LSP) Establishment Using
        RSVP-TE", draft-ietf-mpls-rsvpte-attributes-05 (work in
        progress), May 2005.

   [4]  Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS)
        Signaling Resource ReserVation Protocol-Traffic Engineering
        (RSVP-TE) Extensions", RFC 3473, January 2003.

   [5]  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.

   [6]  Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
        Authentication", RFC 2747, January 2000.

9.2  Informative References

   [7]   Aggarwal, R., "Extensions to RSVP-TE for Point to Multipoint TE
         LSPs", draft-ietf-mpls-rsvp-te-p2mp-01 (work in progress),
         January 2005.

   [8]   Ayyangar, A. and J. Vasseur, "Inter domain GMPLS Traffic
         Engineering - RSVP-TE extensions",
         draft-ietf-ccamp-inter-domain-rsvp-te-00 (work in progress),
         February 2005.

   [9]   Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
         D., Li, T., and A. Conta, "MPLS Label Stack Encoding",
         RFC 3032, January 2001.

   [10]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in
         Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)",
         RFC 3477, January 2003.

   [11]  Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in
         MPLS Traffic Engineering", draft-ietf-mpls-bundle-06 (work in



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         progress), December 2004.

   [12]  Vasseur, J., "A Per-domain path computation method for
         computing Inter-domain Traffic  Engineering (TE) Label Switched
         Path (LSP)", draft-vasseur-ccamp-inter-domain-pd-path-comp-00
         (work in progress), February 2005.

   [13]  Farrel, A., "Path Computation Element (PCE) Architecture",
         draft-ietf-pce-architecture-00 (work in progress), March 2005.


Authors' Addresses

   Arthi Ayyangar (editor)
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   US

   Email: arthi@juniper.net


   Jean Philippe Vasseur
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA  01719
   US

   Email: jpv@cisco.com






















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