MPLS Working Group Tarek Saad, Ed. Internet-Draft Rakesh Gandhi, Ed. Intended status: Standards Track Zafar Ali Expires: January 22, 2015 Cisco Systems, Inc. Robert H. Venator Defense Information Systems Agency Yuji Kamite NTT Communications Corporation July 21, 2014 Reoptimization of Point-to-Multipoint Traffic Engineering Loosely Routed LSPs draft-tsaad-mpls-p2mp-loose-path-reopt-03 Abstract For a Traffic Engineered (TE) point-to-multipoint (P2MP) Label Switched Path (LSP), it is preferable in some cases to re-evaluate and re-optimize the entire P2MP-TE LSP by re-signaling all its S2L sub-LSP(s). Existing mechanisms allow the path re-evaluation and the signaling of a the notification of preferred path exists for a single S2L sub-LSP only. This document defines RSVP-TE signaling extensions to allow an ingress Label Switching Router (LSR) of a P2MP-TE LSP to trigger the re-evaluation of the entire LSP tree containing one or more S2L sub- LSPs whose paths are loose (or abstract) hop expanded, and for a mid- point LSR to signal to the ingress LSR that a better tree exists for the entire P2MP-TE LSP. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." Saad, et al. Expires January 22, 2015 [Page 1] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Nomenclatures . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Conventions used in this document . . . . . . . . . . . . 5 3. Signaling Procedure For Loosely Routed P2MP-TE LSP Reoptimization . . . . . . . . . . . . . . . . . . . . . . . . 5 4. RSVP Signaling Extensions . . . . . . . . . . . . . . . . . . 6 4.1. P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . 6 4.2. Preferable P2MP-TE Tree Exists Path Error sub-code . . . . 6 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7.1. P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . 8 7.2. Preferable P2MP-TE Tree Exists Path Error sub-code . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Saad, et al. Expires January 22, 2015 [Page 2] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 1. Introduction This document defines Resource Reservation Protocol - Traffic Engineering (RSVP-TE) [RFC2205] [RFC3209] signaling extensions for re-optimizing loosely routed Point-to-Multipoint (P2MP) Traffic Engineered (TE) Label Switched Paths (LSPs) [RFC4875] in an Multi-Protocol Label Switching (MPLS) and/or Generalized MPLS (GMPLS) networks. A P2MP-TE LSP is comprised of one or more source-to-leaf (S2L) sub-LSPs. A loosely routed P2MP-TE S2L sub-LSP is defined as one whose path does not contain the full explicit route identifying each node along the path to the egress node at the time of its signaling by the ingress node. Such an S2L sub-LSP is signaled with no Explicit Route Object (ERO) [RFC3209], or with an ERO that contains at least one loose hop, or with an ERO that contains an abstract node that is not a simple abstract node (that is, an abstract node that identifies more than one node). This is often the case with inter-domain P2MP-TE LSPs where Path Computation Element (PCE) is not used [RFC5440]. As per [RFC4875], an ingress node may re-optimize the entire P2MP-TE LSP by re-signaling all its S2L sub-LSP(s) or may re-optimize individual S2L sub-LSP(s) i.e. individual destination(s). [RFC4736] defines RSVP signaling extensions for re-optimizing loosely routed P2P TE LSP(s) as follows. - A mid-point LSR that expands loose next-hop(s) MAY send a solicited or unsolicited PathErr with the Notify error code (25 as defined in [RFC3209]) with sub-code 6 to indicate "Preferable Path Exists" to the ingress node. - An ingress node MAY trigger a path re-evaluation request at all mid-point LSR(s) that expands loose next-hop(s) by setting the "Path Re-evaluation Request" flag (0x20) in SESSION_ATTRIBUTES object in the Path message. - The ingress node upon receiving this PathErr either solicited or unsolicited initiates re-optimization of the LSP. [RFC4736] does not define signaling extensions specific for re- optimizing entire P2MP-TE LSP tree. Mechanisms defined in [RFC4736] can be used for signaling the re-optimization of individual S2L sub- LSP(s). However, to use [RFC4736] mechanisms for re-optimizing an entire P2MP-TE LSP tree, an ingress node needs to send the path re- evaluation requests on all (typically 100s of) S2L sub-LSPs and the Saad, et al. Expires January 22, 2015 [Page 3] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 mid-point LSR to notify PathErrs for all S2L sub-LSPs. Such a procedure may lead to the following issues: - A mid-point LSR that expands loose next-hop(s) may have to accumulate the received path re-evaluation request(s) for all S2L sub-LSPs (e.g, by using a wait timer) and interpret them as a re- optimization request for the whole P2MP-TE LSP tree. Otherwise, A mid-point LSR may prematurely notify "Preferable Path Exists" for one or a sub-set of S2L sub-LSPs. - The ingress LSR that receives (un)solicited PathErr notification(s) for individual S2L sub-LSP(s), may prematurely start re-optimizing the sub-set of S2L sub-LSPs. However, as mentioned in [RFC4875] Section 14.2, such re-optimization procedure may result in data duplication that can be avoided if the entire P2MP-TE LSP tree is re- optimized, especially if the ingress node eventually receives PathErr notifications for all S2L sub-LSPs of the P2MP-TE LSP tree. - The ingress node may have to heuristically determine when to perform entire P2MP-TE LSP tree re-optimization versus per S2L sub- LSP re-optimization, for example, to delay re-optimization long enough to allow all PathErr(s) to be received. Once all PathErr(s) are received, the ingress node has to accumulate them to see if re- optimization of the entire P2MP-TE is necessary. Such procedures may produce undesired results due to timing related issues. This may be easily avoided by the RSVP signaling messages defined in this document. This document defines RSVP-TE signaling extensions for the head-end LSR of a P2MP-TE LSP to trigger the re-evaluation of the P2MP tree on every hop that has a next hop defined as a loose or abstract hop for one or more S2L sub-LSP path, and a mid-point LSR to signal to the head-end LSR that a better tree exists (compared to the current path) or that the whole P2MP-TE LSP must be re-optimized (because of maintenance required on the TE LSP path). 2. Terminology 2.1. Abbreviations ABR: Area Border Router. AS: Autonomous System. ERO: Explicit Route Object. TE LSP: Traffic Engineering Label Switched Path. Saad, et al. Expires January 22, 2015 [Page 4] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 TE LSP ingress: head/source of the TE LSP. TE LSP egress: tail/destination of the TE LSP. Saad, et al. Expires January 22, 2015 [Page 5] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 2.2. Nomenclatures Domain: Routing or administrative domain such as an IGP area and an autonomous system. Interior Gateway Protocol Area (IGP Area): OSPF Area or IS-IS level. Inter-area TE LSP: A TE LSP whose path transits across at least two different IGP areas. Inter-AS MPLS TE LSP: A TE LSP whose path transits across at least two different Autonomous Systems (ASes) or sub-ASes (BGP confederations). S2L sub-LSP: Source-to-leaf sub Label Switched Path. 2.3. 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 [RFC2119]. The reader is assumed to be familiar with the terminology in [RFC4875] and [RFC4736]. 3. Signaling Procedure For Loosely Routed P2MP-TE LSP Re-Optimization It might be preferable, as per [RFC4875], to re-optimize the entire P2MP-TE LSP by re-signaling all of its S2L sub-LSP(s) (Section 14.1, "Make-before- Break") or re-optimize individual S2L sub-LSP(s) i.e. individual destination(s) (Section 14.2 "Sub-Group-Based Re- Optimization"). This can be achieved by using the procedures defined in [RFC4736] to individually re-optimize the S2L sub-LSP(s) of a P2MP-TE LSP. To evaluate an entire P2MP-TE LSP tree on mid-point LSRs that expand loose next-hop(s), an ingress node may send a Path message with "P2MP-TE Tree Re-evaluation Request" defined in this document. An ingress node may select one or more S2L sub-LSP of the P2MP-TE LSP tree to trigger the re-evaluation request(s). A mid-point LSR that expands loose next-hop(s) for one or more S2L sub-LSP path(s), and that receives a Path message with the "P2MP-TE Tree Re-evaluation Request" bit set, checks for a preferable P2MP-TE LSP tree by re-evaluating all S2L sub-LSP(s) expanded paths of the P2MP-TE LSP. If a preferable P2MP-TE LSP tree is found, the mid- point LSR sends an RSVP PathErr to the ingress node with Error code 25 (Notify defined in [RFC3209] and Error sub-code defined in this document "Preferable P2MP-TE Tree Exists". The mid-point LSR, in Saad, et al. Expires January 22, 2015 [Page 6] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 turn, does not propagate the "P2MP-TE Tree Re-evaluation Request" bit in subsequent RSVP Path messages sent downstream for the re-evaluated P2MP-TE LSP. The sending of an RSVP PathErr Notify message "Preferable P2MP-TE Tree Exists" to the ingress node will notify the ingress node of the existence of a preferable P2MP-TE LSP tree. In addition, a mid-point LSR may send an unsolicited PathErr message with "Preferable P2MP-TE Tree Exists" PathErr code 25 to the ingress node to notify of a preferred the P2MP-TE LSP tree when it determines it exists. In this case, the mid-point LSR that expands loose next- hop(s) for one or more S2L sub-LSP path(s) may select one or more S2L sub-LSP(s) of the P2MP-TE LSP tree to send this PathErr message to the ingress node. If no preferable tree for P2MP-TE LSP can be found, the recommended mode is for the mid-point LSR that expands loose next-hop(s) for one or more S2L sub-LSP path(s) to propagate the request downstream by setting the "P2MP-TE Tree Re-evaluation Request" bit in the LSP_ATTRIBUTES object of RSVP Path message. 4. RSVP Signaling Extensions 4.1. P2MP-TE Tree Re-evaluation Request Flag In order to trigger a tree re-evaluation request, a new flag is defined in Attributes Flags TLV of the LSP_ATTRIBUTES object [RFC5420] as follows: Bit Number (to be assigned by IANA): P2MP-TE Tree Re-evaluation Request flag The "P2MP-TE Tree Re-evaluation Request" flag is meaningful in a Path message of a P2MP-TE S2L sub-LSP and is inserted by the ingress node. 4.2. Preferable P2MP-TE Tree Exists Path Error sub-code In order to indicate to an ingress node that a preferable P2MP-TE LSP tree exists, the following new sub-code for PathErr code 25 (Notify Error) [RFC3209] is defined: Sub-code (to be assigned by IANA): Preferable P2MP-TE Tree Exists sub-code When a preferable path for P2MP-TE LSP tree exists, the mid-point LSR sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists" PathErr notification to the ingress node of the P2MP-TE LSP. Saad, et al. Expires January 22, 2015 [Page 7] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 5. Compatibility The LSP_ATTRIBUTES object has been defined in [RFC5420] with class numbers in the form 11bbbbbb, which ensures compatibility with non-supporting nodes. Per [RFC2205], nodes not supporting this extension will ignore the new flag defined in this document but forward it without modification. 6. Security Considerations This document defines a mechanism for a mid-point LSR to notify the ingress node of a P2MP-TE LSP of the existence of a preferable tree. As per [RFC4736], in the case of a P2MP-TE LSP S2L sub-LSP spanning multiple domains, it may be desirable for a a mid-point LSR to modify the RSVP PathErr message defined in this document to maintain confidentiality across different domains. Furthermore, an ingress node may decide to ignore this PathErr message coming from a mid- point LSR residing in another domain. Similarly, an mid-point LSR may decide to ignore the tree re-evaluation request originating from another ingress domain. 7. IANA Considerations IANA maintains a name space for RSVP-TE TE parameters "Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters". From the registries in this name space "Attribute Flags" allocation of new flag is requested (Section 4.1). IANA also maintains a name space for RSVP protocol parameters "Resource Reservation Protocol (RSVP) Parameters". From the sub- registry "Sub-Codes - 25 Notify Error" in registry "Error Codes and Globally-Defined Error Value Sub-Codes" allocation of a new error code is requested (Section 4.2). Saad, et al. Expires January 22, 2015 [Page 8] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 7.1. P2MP-TE Tree Re-evaluation Request Flag The following new flag is defined for the Attributes Flags TLV in the LSP_ATTRIBUTES object [RFC5420]. The numeric value is to be assigned by IANA. o P2MP-TE Tree Re-evaluation Request Flag: +--------+---------------+---------+---------+---------+------------+ | Bit No | Attribute | Carried | Carried | Carried | Reference | | | Flag Name | in Path | in Resv | in RRO | | +--------+---------------+---------+---------+---------+------------+ | TBA by | P2MP-TE Tree | Yes | No | No | This | | IANA | Re-evaluation | | | | document | +--------+---------------+---------+---------+---------+------------+ 7.2. Preferable P2MP-TE Tree Exists Path Error sub-code As defined in [RFC3209], the Error Code 25 in the ERROR SPEC object corresponds to a Notify Error PathErr. This document adds a new sub-code as follows for this PathErr: o Preferable P2MP-TE Tree Exists sub-code: +----------+--------------------+---------+---------+-----------+ | Sub-code | Sub-code | PathErr | PathErr | Reference | | value | Name | Code | Name | | +----------+--------------------+---------+---------+-----------+ | TBA by | Preferable P2MP-TE | 25 | Notify | This | | IANA | Tree Exists | | error | document | +----------+--------------------+---------+---------+-----------+ 8. Acknowledgments The authors would like to thank Loa Andersson for reviewing this document. Saad, et al. Expires January 22, 2015 [Page 9] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 9. References 9.1. Normative References [RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [RFC3209] 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. [RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007. [RFC5420] Farrel, A., Papadimitriou, D., Vasseur, JP., and A. Ayyangarps, "Encoding of Attributes for MPLS LSP Establishment Using Resource Reservation Protocol Traffic Engineering (RSVP-TE)", RFC 5420, February 2009. 9.2. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4736] Vasseur, JP., Ikejiri, Y. and Zhang, R, "Reoptimization of Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) Loosely Routed Label Switched Path (LSP)", RFC 4736, November 2006. [RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. Saad, et al. Expires January 22, 2015 [Page 10] Internet-Draft P2MP-TE Loosely Routed LSPs July 21, 2014 Author's Addresses Tarek Saad (editor) Cisco Systems Email: tsaad@cisco.com Rakesh Gandhi (editor) Cisco Systems Email: rgandhi@cisco.com Zafar Ali Cisco Systems Email: zali@cisco.com Robert H. Venator Defense Information Systems Agency Email: robert.h.venator.civ@mail.mil Yuji Kamite NTT Communications Corporation Email: y.kamite@ntt.com Saad, et al. Expires January 22, 2015 [Page 11]