Internet Draft Network Working Group Atsushi Iwata Internet Draft Norihito Fujita <draft-iwata-mpls-crankback-rsvp-te-00.txt> NEC Corporation Expiration Date: June 2001 Gerald R. Ash AT&T Adrian Farrel Data Connection Ltd. December 2000 Crankback Routing Extensions for MPLS Signaling with RSVP-TE <draft-iwata-mpls-crankback-rsvp-te-00.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 1] Internet Draft December 2000 Abstract This draft proposes crankback routing extensions for RSVP-TE signaling and in a companion document for CRLDP signaling. Recently, several routing protocol extensions for advertising resource information in addition to topology information have been proposed for use in distributed constraint-based routing. In such a distributed routing environment, however, the information used to compute a constraint-based path may be out of date. This means that LSP setup requests may be blocked by links or nodes without sufficient resources. This draft specifies crankback routing extensions for CR-LDP and RSVP-TE so that the label request can be retried on an alternate path that detours around the blocked link or node upon a setup failure. Furthermore, the crankback routing schemes can also be applied to LSP restoration by indicating the location of the failure link or node. This would significantly improve the successful recovery ratio for failed LSPs, especially in situations where a large number of setup requests are triggered at the same time. Table of Contents Page 1. Introduction 3 2. RSVP-TE considerations 4 2.1 Indication of Rerouting Behavior 6 2.2 Rerouting Object 7 2.3 Link-Rerouting Subobject 8 2.4 Node-Rerouting Subobject 11 2.5 Error Values 13 2.6 ResvErr Usage 13 2.7 Notify Message Usage 13 2.8 Backward Compatibility 14 3. Security Considerations 15 4. Acknowledgments 15 5. References 15 Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 2] Internet Draft December 2000 1. Introduction CR-LDP (Constraint-based Routing Label Distribution Protocol) [CR- LDP] and RSVP-TE (RSVP Extension for LSP Tunnel) [RSVP-TE] can be used for establishing explicitly routed LSPs (CR-LSPs) in an MPLS network. Using CR-LDP and RSVP-TE, resources can also be reserved along a path to guarantee or control QoS for traffic carried on the LSP. To designate an explicit path that satisfies QoS constraints, it is necessary to discern the resources available to each link or node in the network. For the collection of such resource information, routing protocols, such as OSPF [OSPF] and IS-IS [ISIS], can be extended to distribute additional state information [AWDUCHE1]. Explicit paths can be designated based on the distributed information at the LSR initiating a LSP and, if necessary, intermediate area border LSRs. In a distributed routing environment, however, the resource information used to compute a constraint-based path may be out of date. This means that a setup request may be blocked, for example, because a link or node along the selected path has insufficient resources. In the current CR-LDP specification, when an LSP setup failure occurs, a Notification message is returned to the setup initiator (ingress LSR), which terminates this message and gives up the LSP establishment. In RSVP-TE, a blocked LSP setup may result in a PathErr message sent to the initiator or a ResvErr sent to the terminator (egress LSR). These messages may result in the LSP setup being abandoned. In Generalized MPLS [GMPLS] the Notify message can be used in RSVP-TE networks to expedite notification of LSP failures to ingress and egress LSRs, or to a specific "repair point". If the ingress or intermediate area border LSR knows the location of the blocked link or node, the LSR can designate an alternate path and then reissue the setup request, which can be achieved by the mechanism known as crankback routing [PNNI, ASH1, ASH2]. We propose the use of crankback routing in RSVP-TE and, in a companion document, in CRLDP [CRNKBK-CRLDP]. Crankback routing requires notifying an upstream LSR of the location of the blocked link or node. On the other hand, various restoration schemes for link or node failures have been proposed in [MAKAM, SHARMA] and others. Fast restoration by pre-establishing a backup LSP is useful for failures on a primary LSP. If both the primary and backup paths fail, however, it is necessary to reestablish the LSP on an end-to-end basis. End- to-end restoration for alternate routing requires the location of the failed link or node. The crankback routing schemes could also be used to notify upstream LSRs of the location of the failure, and this notification would likely occur more quickly than for the IGP to detect the failure and reconverge to new routing around the failure. Furthermore, in situations where many link or node failures occur at the same time, the difference between the distributed routing information and the real-time network state becomes much greater than Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 3] Internet Draft December 2000 in normal LSP setups. The LSP restoration must therefore be performed with inaccurate information, which is likely to cause setup blocking. Crankback routing would also improve failure recovery in these situations. Recently, Multi-Protocol Lambda Switching has also been discussed [AWDUCHE2]. In a network without wavelength converters, setup requests are likely to be blocked more often than in a conventional MPLS environment because the same wavelength must be allocated at each OXC on an end-to-end explicit path. Furthermore, end-to-end restoration is the only way to recover LSP failures [CHAUDHURI]. This implies that crankback routing would also be useful in an MPLambdaS network, and again, the use of crankback could result in selecting an alternate path more quickly in a failure situation. This draft proposes a crankback routing system that is an extension of RSVP-TE, and of CRLDP in [CRNKBK-CRLDP], and discusses the identification of blocked links or nodes in an MPLS network. See [CRNKBK-CRLDP] for a general discussion of crankback functionality, including o explicit versus implicit rerouting, o crankback routing behaviors due to LSP setup blockage, o new status codes for rerouting, location identifiers of blocked links or nodes, and o LSP restoration considerations. In the following sections we identify the specific protocol extensions for crankback functionality within RSVP-TE. 2. RSVP-TE considerations Nothing precludes the use of crankback routing mechanism and LSP restoration mechanism with appropriate TLV structures in the RSVP-TE messages. We illustrate a simple case of setting up an LSP on an explicit route from router-A to router-B, in which certain Tspec and Flowspec requirements must be met on each link in the LSP. The steps are as follows [RSVP][RSVP-TE]: (1) router-A (ingress LSR) sends an RSVP Path message to router-B (egress LSR) with a) a TSPEC object that specifies the traffic characteristics of the data flow that the route-A will generate on the LSP Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 4] Internet Draft December 2000 b) an EXPLICIT_ROUTE object (ERO) that specifies the explicit route of the LSP (2) along the way accumulate Adspec to describe the network resources available (3) at the router-B (the egress LSR) map these to an Rspec to build a FLOWSPEC object which includes a service class and the TSPEC object and the RSPEC object. (4) router-B sends the FLOWSPEC object back in a Resv message along the specified explicit route, hop-by-hop in reverse order and reserves the resources link by link Resource allocation failure may occur at two points. (a) On the reverse path, as the Resv is processed, resources are reserved and, if they are not available on the required link or at a specific node, a ResvErr message is returned to the egress node (router-B) indicating "Admission Control failure" [RSVP]. Router-B is allowed to change the Rspec and try again, but in the event that this is not practical or not supported, router-B may choose to take any one of the following actions. - Ignore the situation and allow recovery to happen through Path refresh and refresh timeout [RSVP]. - Send a PathErr towards router-A indicating "Admission Control failure". - Send ResvTear towards router-A to abort the LSP setup. (b) It is also possible to make resource reservations on the forward path as the Path message is processed. This choice is made in many RSVP-TE implementations and is compatible with LSP setup in optical networks [GMPLS]. In this case if resources are not available, a PathErr message is returned to router-A indicating "Admission Control failure". Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 5] Internet Draft December 2000 2.1 Indication of Rerouting Behavior The behavior specified by the RtgFlg described in Section 6 of [CRNKBK-CRLDP] is achieved in RSVP-TE by a change to the LSP_TUNNEL Session Attribute Object. A new RtgFlg field is added in what was previously a reserved area in the object. The object is now specified as follows. class = SESSION_ATTRIBUTE, LSP_TUNNEL C-Type = 7 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Setup Prio | Holding Prio | Flags | Name Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Session Name (NULL padded display string) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Setup Priority The priority of the session with respect to taking resources, in the range of 0 to 7. The value 0 is the highest priority. The Setup Priority is used in deciding whether this session can preempt another session. Holding Priority The priority of the session with respect to holding resources, in the range of 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. Flags 0x01 Local protection desired This flag permits transit routers to use a local repair mechanism which may result in violation of the explicit route object. When a fault is detected on an adjacent downstream link or node, a transit router can reroute traffic for fast service restoration. 0x02 Label recording desired This flag indicates that label information should be included when doing a route record. 0x04 SE Style desired Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 6] Internet Draft December 2000 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. 0x08 End-to-end rerouting desired This flag indicates the end-to-end rerouting behavior for an LSP under establishment. This can also be used for specifying the behavior of end-to-end LSP restoration for established LSPs. 0x10 Segment-based rerouting (hierarchical rerouting) desired. This flag indicates the segment-based rerouting (hierarchical rerouting) behavior for an LSP under establishment. This can also be used for specifying the segment-based (hierarchical) LSP restoration for established LSPs. Name Length The length of the display string before padding, in bytes. Session Name A null padded string of characters. 2.2 Rerouting Object We define a new object, the "rerouting Object", analagous to the "Rerouting TLV" defined in Section 7.1 of [CRNKBK-CRLDP], to explicitly indicate that crankback rerouting is allowed at router-A. The new object is added to the definition of the PathErr message specifying it as optional. When a PathErr message carrying the Rerouting object is received at router-A, router-A MAY attempt crankback rerouting. It can choose from the following actions. - Send PathTear to give up - Do nothing to give up (soft state times out) - Pick a new route and send a new Path - Change the resource requirements and send a new Path message The PathErr message is defined as follows: Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 7] Internet Draft December 2000::= [ ] [ ] [ ...] [ ] The Rerouting Object is defined as follows: IPv4 REROUTING object: Class = TBD, C-Type = 1 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (Subobjects) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Rerouting object may contain one or more subobjects of the following types: Link Rerouting Subobject: See below for the format. Node Rerouting Subobject: See below for the format. 2.3 Link-Rerouting Subobject This subobject is analogous to the Link TLV in Sec.7.2 of [CRNKBK-CRLDP]. It may be carried in the Rerouting object in a PathErr message. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Protocol Type | Num | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Identifier Components 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ............ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Identifier Components N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The Type indicates the type of contents of the subobject. 1 Link-Rerouting subobject Length The length in bytes of the subobject Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 8] Internet Draft December 2000 Protocol Type A one-octet unsigned integer containing the unique identifier of a protocol used for QoS routing. The following type numbers are defined. If a constraint-based route is to be calculated with no routing protocols, type 1 should be used. A location is identified using the ERO, independent of protocols. If a type other than 1 is used, or the routing-protocol-specific link identifiers are used, the Flag of the SESSION_ATTRIBUTE in the LSP_TUNNEL_IPv4 Session Object carried in the Path message must be set 0x10, which implies that segment-based rerouting (hierarchical rerouting) is used. 1: RSVP-TE for IPv4 (EXPLICIT ROUTE Object) 2: OSPFv2 for IPv4 [OSPF] 3: Integrated IS-IS (or IS-IS) for IPv4 [ISIS] 4: OSPF for IPv6 [OSPF6] 5: Integrated IS-IS (or IS-IS) for IPv6 [ISIS6] 128-255: Reserved for private and experimental use. Num: Number of Link Identifier Components A one-octet unsigned integer specifying the number of Link Identifier Components included in the object. One or more Link Identifier Components A variable length field containing link identifiers for relevant protocol types. When the type is RSVP-TE for IPv4 (1), the following format is used. The first and second ERO hop upon setup blockage are included. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First ERO hop | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Second ERO hop | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ When the protocol type is OSPFv2 for IPv4 (2), the following 8-octet format is used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 9] Internet Draft December 2000 Router ID The same value as the Router ID used in OSPFv2 for IPv4. Link ID The same value as the Link ID used in OSPFv2 for IPv4. When the protocol type is OSPF for IPv6 (4), the following 8-octet format is used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Router ID The same value as the Router ID used in OSPF for IPv6. Interface ID The same value as the Interface ID used in OSPF for IPv6. When the protocol type is IS-IS for IPv4 (3), the following 12-octet format is used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ System ID The same value as System ID used in IS-IS for IPv4 (3). IP Interface Address The IP address assigned to the interface advertised in IS-IS for IPv4 (3). When the protocol type is IS-IS for IPv6 (5), the following 24-octet format is used. Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 10] Internet Draft December 2000 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + | | | + IP Interface Address | | | + | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ System ID The same value as System ID used in IS-IS for IPv6 (5). IP Interface Address The IP address assigned to the interface advertised in IS-IS for IPv6 (5). 2.4 Node-Rerouting Subobject This subobject is analogous to the Node TLV in Sec.7.3 of [CRNKBK-CRLDP]. It may be carried in the Rerouting object in a PathErr message. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Protocol Type | Num | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Node Identifier Components 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ............ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Node Identifier Components N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The Type indicates the type of contents of the subobject. 2 Node-Rerouting subobject Length The length in bytes of the subobject Protocol Type Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 11] Internet Draft December 2000 A one-octet unsigned integer containing the unique identifier of the protocol used for QoS routing. The same value as defined in the Link-Rerouting subbject is used. Num: Number of Node Identifier Components A one-octet unsigned integer specifying the number of Node Identifier Components included in the object. One or mode Node Identifier Components A variable length field containing the node identifier for relevant protocol types. When the type is RSVP-TE for IPv4 (1), the following format is used. The first ERO Hop upon setup blockage is included. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | First ERO Hop | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ When the protocol type is OSPFv2 for IPv4 (2) or OSPF for IPv6 (4), the following 4-octet format is used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Router ID The same value as the Router ID used in OSPFv2 for IPv4 or in OSPF for IPv6. When the protocol type is IS-IS for IPv4 (3) or IS-IS for IPv6 (5), the following 8-octet format is used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System ID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ System ID The same value as the System ID used in IS-IS for IPv4 (3) or in Iwata, et al. draft-iwata-mpls-crankback-rsvp-te-00.txt [Page 12] Internet Draft December 2000 IS-IS for IPv6 (5). 2.5 Error Values Error values for the Error Code "Admission Control Failure" are defined in [RSVP]. It may be appropriate to define new additional subcodes to provide additional action information. This area is for future study. 2.6 ResvErr Usage As described above, the resource allocation failure for RSVP-TE may occur when the reverse path when the Resv message is being processed. In this case, it is still useful to collect the crankback information and return it to the ingress LSR. This can be achieved by specifying additions to the ResvErr message as follows. ::= [ ] [ ] [ ] [ ...]