Network Working Group A. Ayyangar, Ed. Internet-Draft Nuova Systems Intended status: Standards Track K. Kompella, Ed. Expires: June 5, 2007 Juniper Networks
Expires: September 6, 2006JP. Vasseur Cisco Systems, Inc. March 5,December 2, 2006 Label Switched Path Stitching with Generalized MPLS Traffic Engineering draft-ietf-ccamp-lsp-stitching-03.txtdraft-ietf-ccamp-lsp-stitching-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 6, 2006.June 5, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract In certain scenarios, there may be a need to combine together differentseveral Generalized Multi-Protocol Label Switching (GMPLS) Label Switched Paths (LSPs) such that in the data plane,a single end-to- endend-to-end (e2e) LSP is realized and all traffic from one constituent LSP is switched onto the othernext LSP. We will refer to this as "LSP stitching". This document covers cases where: a)stitching", the node performing the stitching does not require configuration of everykey requirement being that a constituent LSP pair to be stitched together b) the node performing the stitching isnot the egress of any of thebe allocated to more than one e2e LSP. The constituent 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.will be referred to as "LSP segments" (S-LSPs). 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 . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.1. Conventions used in this document . . . . . . . . . . . . 34 2. Comparison with LSP Hierarchy . . . . . . . . . . . . . . . . 45 3. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.1. Triggers for LSP segment setup . . . . . . . . . . . . . . 56 3.2. Applications . . . . . . . . . . . . . . . . . . . . . . . 56 4. Routing aspects . . . . . . . . . . . . . . . . . . . . . . . 67 5. Signaling aspects . . . . . . . . . . . . . . . . . . . . . . 79 5.1. RSVP-TE signaling extensions . . . . . . . . . . . . . . . 79 5.1.1. Creating and preparing LSP segment for stitching . . . 79 5.1.2. Stitching the e2e LSP to the LSP segment . . . . . . . 911 5.1.3. RRO Processing for e2e LSP . . . . . . . . . . . . . . 1012 5.1.4. Teardown of LSP segment . . . . . . . . . . . . . . . 1113 5.1.5. Teardown of e2e LSP . . . . . . . . . . . . . . . . . 1113 5.2. Summary of LSP Stitching procedures . . . . . . . . . . . 1214 5.2.1. Example topology . . . . . . . . . . . . . . . . . . . 1214 5.2.2. LSP segment setup . . . . . . . . . . . . . . . . . . 1215 5.2.3. Setup of e2e LSP . . . . . . . . . . . . . . . . . . . 1315 5.2.4. Stitching of e2e LSP into an LSP segment . . . . . . . 1315 6. Security Considerations . . . . . . . . . . . . . . . . . . . 1416 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 1517 7.1. Attribute Flags for LSP_ATTRIBUTES object . . . . . . . . 1517 7.2. New Error Codes . . . . . . . . . . . . . . . . . . . . . 1517 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 1618 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 1719 9.1. Normative References . . . . . . . . . . . . . . . . . . . 1719 9.2. Informative References . . . . . . . . . . . . . . . . . . 1719 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 1921 Intellectual Property and Copyright Statements . . . . . . . . . . 2022 1. Introduction This document describes the mechanisms to accomplish LSP stitching in the scenarioscontrol (routing and signaling) and data planes, contrasting stitching with LSP hierarchy () as is meaningful. With the mechanism described above.here, the node performing the stitching does not require configuration of the pair of LSPs to be stitched together. Also, LSP stitching as defined here results in an end-to-end LSP both in the control and data planes. LSP hierarchy () provides signaling and routing procedures so that: a. A Hierarchical LSP (H-LSP) can be created. Such an LSP created in one layer can provideappear as a data link to LSPs in higher layers. AlsoAs such, one or more LSPs in a higher layer can be nested intotraverse this H-LSP as a single hop; we call this H-LSP."nesting". 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 . 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 so advertised, other GMPLS nodes could usedcan use 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.Thus, if LSP-AB is an H-LSP between nodes A and B, then multiple LSPs, say LSP1, LSP2, and LSP3 couldcan potentially be 'nested into' LSP-AB. This is achieved by exchanging a unique label for each of LSP1..3 over the LSP-AB hophop, thereby permitting LSP1..3separating the data corresponding to shareeach of LSP1..3 while traversing 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 LSP1LSP1, may be stitched to the S-LSP LSP-AB. LSP-AB is then 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, similar to H-LSPs, several S-LSPs MAYmay be bundled into a TE link (), 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)(non-adjacent) RSVP signaling defined in  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. 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 () defines one possible trigger for dynamic creation of FA-LSP by introducing the notion of LSP regions based on Interface Switching Capabilities. As per , 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 . 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.E.g., if an e2e lambda LSP traverses an LSP segment TE link which is also lambda switch capable, then in this caseLSP hierarchy is not possible.possible; in this case, LSP switching may be an option. LSP stitching procedures couldcan be used for inter-domain TE LSP signaling to stitch an inter-domain e2e LSP to a local intra-domain TE S-LSP (). LSP stitching couldmay 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.E.g., one suggested usage in case of P2MP RSVP LSPs () 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. 4. Routing aspects An S-LSP is created between two GMPLS nodes and it may traverse zero or more intermediate 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  SHOULD be used. ISIS/OSPF may floodWhen appropriate, the TE information associated with an S-LSP TE link, when appropriate.link MAY be flooded via ISIS-TE  or OSPF-TE . 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. When so advertising S-LSPs, one should keep in mind that these add to the size and complexity of the link-state database. 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  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, multipleIf an S-LSP is allocated to an e2e LSP, the unreserved bandwidth SHOULD be set to zero to prevent further e2e LSPs being admitted into the S-LSP. Multiple S-LSPs between the same pair of nodes MAY be bundled using the concept of Link Bundling () into a single TE link. So, while anIn this case, each component S-LSP can have exactly one e2e LSP associated with it, a bundled TE link comprising of multiple S-LSPs, MAY admit more thanmay be allocated to at most 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. 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 . In order to signal an e2e LSP over an LSP segment, signaling procedures described in section 8.1.1 of  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 (), to an S-LSP. Stitching an e2e LSP to an LSP segment involves the following two step process: a.1. Creating and preparing the S-LSP for stitching by signaling the desire to stitch between end points of the S-LSPS-LSP; and b. Stitching2. stitching the e2e LSP to the S-LSPS-LSP. 5.1.1. Creating and preparing LSP segment for stitching If a GMPLS node desires to perform LSPcreate an S-LSP, i.e., one to be used for stitching, then it MUST indicate this in the Path message for the S-LSP that it plans to use for stitching.S-LSP. 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 : 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. 184.108.40.206. 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 () in the Resv Label. These steps MUST NOT be used for a non-packet LSP and for packet LSPs where 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 or Explicit 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. If the e2e LSP and the S-LSP are bidirectional, the ingress of the e2e LSP SHOULD first check whether it is also the ingress of the S-LSP. If so, it SHOULD re-issue the Path message for the S-LSP with an implicit or explicit NULL upstream label; and only then proceed with the signaling of the e2e LSP. 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  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  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  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 . 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 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 . 5.1.3. 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 () 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  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 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  and . 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  and  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  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 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 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 adevrtisedadvertised 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 ()() or PCE based computation ()() 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 the S-LSP LSP-AB to stitchwhich LSP1-2 towill be stitched has been determined successfully,determined, the Path message for LSP1-2 is sent (via IP routedrouting, if needed) 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 routedsent 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. 6. Security Considerations Similar to , 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  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,  should be revisited to check if IPSec AH is now a viable means of securing RSVP-TE messages. 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. 8. Acknowledgments The authors would like to thank Adrian Farrel and Kireeti Kompellafor theirhis 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. 9. References 9.1. Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.  Farrel, A., Papadimitriou, D., Vasseur, J., and A. Ayyangar, "Encoding of Attributes for Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Establishment Using Resource ReserVation Protocol-Traffic Engineering (RSVP-TE)", RFC 4420, February 2006.  Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.  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.  Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic Authentication", RFC 2747, January 2000. 9.2. Informative References  Aggarwal, R., "Extensions to RSVP-TE for Point to MultipointPoint-to-Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-p2mp-01draft-ietf-mpls-rsvp-te-p2mp-06 (work in progress), January 2005.August 2006.  Ayyangar, A. and J. Vasseur, "Inter domain GMPLS Traffic Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter-domain-rsvp-te-00draft-ietf-ccamp-inter-domain-rsvp-te-03 (work in progress), February 2005.March 2006.  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, January 2001.  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, January 2003.  Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.  Kompella, K. and Y. Rekhter, "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, October 2005.  Kompella, K. and Y. Rekhter, "Intermediate System to Intermediate System (IS-IS) Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4205, October 2005.  Vasseur, J., "A Per-domain path computation method for computingestablishing Inter-domain Traffic Engineering (TE) Label Switched Path (LSP)", draft-ietf-ccamp-inter-domain-pd-path-comp-00Paths (LSPs)", draft-ietf-ccamp-inter-domain-pd-path-comp-03 (work in progress), April 2005. August 2006.  Farrel, A., "Path"A Path Computation Element (PCE) Based Architecture", draft-ietf-pce-architecture-00draft-ietf-pce-architecture-05 (work in progress), March 2005.April 2006. Authors' Addresses Arthi Ayyangar (editor) Nuova Systems 2600 San Tomas Expressway Santa Clara, CA 95051 US Email: email@example.com Kireeti Kompella (editor) Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: firstname.lastname@example.org@juniper.net Jean Philippe Vasseur Cisco Systems, Inc. 300 Beaver Brook Road Boxborough, MA 01719 US Email: email@example.com Full Copyright Statement Copyright (C) The Internet Society (2006). 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. 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