Network Working Group X. Xu Internet-Draft M. Chen Intended status: Standards Track Huawei Expires: July 25, 2014 January 21, 2014 Advertising Global Labels or SIDs Using OSPF draft-xu-ospf-global-label-sid-adv-00 Abstract Segment Routing (SR) is a new MPLS paradigm in which each SR-capable router is required to advertise global MPLS labels or Segment IDs (SID) for its attached prefixes by using link-state IGPs, e.g., OSPF. One major challenge associated with such global MPLS label or SID advertisement mechanism is how to avoid a given global MPLS label or SID from being allocated by different routers to different prefixes. Although such global label or SID allocation collision problem can be addressed through manual allocation , it is error-prone and nonautomatic therefore may not be suitable in large-scale SR network environments. This document proposes an alternative approach for allocating and advertising global MPLS labels or SIDs via OSPF so as to eliminate the potential risk of label allocation collision. 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." This Internet-Draft will expire on July 25, 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 Xu & Chen Expires July 25, 2014 [Page 1] Internet-Draft January 2014 (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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Advertising Label Bindings for Prefixes . . . . . . . . . . . 3 4. Advertising SID Bindings for Prefixes . . . . . . . . . . . . 4 5. Requesting Label Bindings for Prefixes . . . . . . . . . . . 5 6. Requesting SID Bindings for Prefixes . . . . . . . . . . . . 5 7. Advertising Mapping Server Capability . . . . . . . . . . . . 5 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 10. Security Considerations . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 11.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Segment Routing (SR) [I-D.filsfils-rtgwg-segment-routing] is a new MPLS paradigm in which each SR-capable router is required to advertise global MPLS labels or Segment IDs (SID) for its attached prefixes by using link-state IGPs, e.g., OSPF[I-D.psenak-ospf-segment-routing-extensions] . One major challenge associated with such global MPLS label or SID advertisement mechanism is how to avoid a given global MPLS label or SID from being allocated by different routers to different prefixes. Although such global label or SID allocation collision problem can be addressed through manual allocation, it is error-prone and nonautomatic therefore may not be suitable in large-scale SR network environments. This document proposes an alternative approach for allocating and advertising global MPLS labels or SIDs via OSPF so as to eliminate the potential risk of label allocation collision. The basic idea of this approach is to allow a particular IGP router to allocate global MPLS labels or SIDs for those prefixes attached to each SR-capable router and meanwhile advertise the corresponding label or SID bindings in the IGP domain scope. That particular IGP rouer is therefore refered to as a mapping server. As for how the mapping Xu & Chen Expires July 25, 2014 [Page 2] Internet-Draft January 2014 server know which prefixes need to be allocated with global labels or SIDs, it can be achieved either by configuration on the mapping server or by advertisement from SR-capable routers. In the multi- area scenario where route summarization between areas is enabled, the IP longest-match algorithm SHOULD be used by SR-capable routers when processing label or SID bindings advertised by the mapping server, just as the mechanism defined in [RFC5283]. 1.1. Requirements Language 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 [RFC2119]. 2. Terminology This memo makes use of the terms defined in [I-D.filsfils-rtgwg-segment-routing] and [RFC4970]. 3. Advertising Label Bindings for Prefixes A new Opaque LSA [RFC5250] of type 11 (with domain-wide flooding scope), referred to as Prefix Opaque LSA, is defined. The opaque type of this Prefix Opaque LSA is TBD. A mapping server could use one or more Prefix Opaque LSAs to advertise label bindings for those prefixes which need to be allocated with global labels. One or more Prefix TLV (type code=TBD) as shown below could be contained in a Prefix Opaque LSA. 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=TBD | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | Prefix-Len | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Prefix (0-4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Sub-TLVs (Variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD. Length: Variable. MT-ID: Multi-Topology ID as defined in [RFC4915]. Prefix-Len: the length of the prefix in bits (i.e., 0-32). Xu & Chen Expires July 25, 2014 [Page 3] Internet-Draft January 2014 IPv4 Prefix: the prefix is encoded in the minimal number of octets (i.e., 0-4) for the given number of significant bits. A Label Binding Sub-TLV (type code=TBD) as shown below is associated with a prefix which is contained in the Prefix TLV. 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=TBD | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P| Reserved | MPLS Label (20 bit) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD. Length: 4. P-Flag: if set, the penultimate hop router MUST perform PHP action on the allocated MPLS label. For a given prefix, the P-Flag in the Label Binding Sub-TLV MUST be set to the same value as that of the P-Flag in the Label Request Sub-TLV if a label request message (see section 5 of this document) for that prefix is received by the mapping server. MPLS Label: a global label which is allocated to the prefix which is contained in the Prefix TLV. 4. Advertising SID Bindings for Prefixes A mapping server could use one or more Prefix Opaque LSAs as defined in Section 3 to advertise SID bindings for those prefixes which need to be allocated with global SIDs. One or more Prefix TLV as defined in Section 3 could be contained in a Prefix Opaque LSA. A SID Binding Sub-TLV (type code=TBD) as shown below is associated with a prefix which is contained in the Prefix TLV. 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=TBD | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD. Xu & Chen Expires July 25, 2014 [Page 4] Internet-Draft January 2014 Length: 4. SID: a SID for the prefix which is carried in the TLV containing this sub-TLV. 5. Requesting Label Bindings for Prefixes SR-capable OSPF routers could use one or more Prefix Opaque LSAs as defined in section 3 of this document to advertise those among their attached prefixes which need to be allocated with global labels. A new Sub-TLV of the Prefix TLV, referred to as Label Request Sub-TLV (type code=TBD) as shown below is associated with a prefix which is contained in a Prefix TLV. 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=TBD | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD. Length: 4. P-Flag: if set, the penultimate hop router MUST perform PHP action on the required label. 6. Requesting SID Bindings for Prefixes SR-capable OSPF routers could use one or more Prefix Opaque LSAs as defined in section 3 of this document to advertise those among their attached prefixes which need to be allocated with global SIDs. A new Sub-TLV of the Prefix TLV, referred to as SID Request Sub-TLV (type code=TBD and Length=0) is associated with a prefix which is contained in a Prefix TLV. 7. Advertising Mapping Server Capability For redundancy purpose, more than one router could be configured as candidates for mapping servers. Each candidate for mapping servers SHOULD advertise its capability of being a mapping servers by using OSPF Router Capability TLV. The one with the highest priority SHOULD be elected as the primary mapping server which is eligible to allocate and advertise global labels or SIDs for prefixes on behalf of SR-capable routers. The comparison of OSPF router ID breaks the tie between two or more candidates with the same highest priority. Xu & Chen Expires July 25, 2014 [Page 5] Internet-Draft January 2014 Meanwhile, the one with the second highest priority SHOULD be elected as a backup mapping server. This backup mapping server SHOULD advertise the same label bindings as those advertised by the primary mapping server. In this way, the unnecessary changes to the data plane (i.e., MPLS forwarding table) of SR-capable routers can be avoided in the event of mapping server failover. Each candidate mapping server SHOULD advertise its capability of being mapping servers by using an OSPF Router Informational Capabilities TLV [RFC4970] contained in an Opaque LSA of type 11 (with domain-wide flooding scope). One of the unreserved OSPF Router Informational Capabilities Bits is reserved for this purpose. Furthermore, a sub-TLV (type code=TBD) as shown below is used to convey the priority value for mapping server election. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Priority | +-+-+-+-+-+-+-+-+ Type: TBD. Length: 1 Priority: the priority for mapping server election. 8. Acknowledgements The authors would like to thank . 9. IANA Considerations TBD. 10. Security Considerations This document does not introduce any new security considerations. 11. References 11.1. Normative References Xu & Chen Expires July 25, 2014 [Page 6] Internet-Draft January 2014 [I-D.psenak-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., and W. Henderickx, "OSPF Extensions for Segment Routing", draft-psenak-ospf-segment-routing- extensions-03 (work in progress), October 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, June 2007. [RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, July 2007. [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, July 2008. [RFC5283] Decraene, B., Le Roux, JL., and I. Minei, "LDP Extension for Inter-Area Label Switched Paths (LSPs)", RFC 5283, July 2008. 11.2. Informative References [I-D.filsfils-rtgwg-segment-routing] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment Routing Architecture", draft-filsfils-rtgwg- segment-routing-01 (work in progress), October 2013. Authors' Addresses Xiaohu Xu Huawei Email: xuxiaohu@huawei.com Mach Chen Huawei Email: mach.chen@huawei.com Xu & Chen Expires July 25, 2014 [Page 7]