Network working group X. Xu Internet Draft M. Chen Category: Standard Track Huawei Expires: January 2014 July 11, 2013 Advertising Global Labels Using IGP draft-xu-rtgwg-global-label-adv-00 Abstract Segment Routing (SR) [SR-ARCH] is a new MPLS paradigm in which each SR-capable router is required to independently advertise global MPLS labels for its attached prefixes using IGP [SR-ISIS-EXT][SR-OSPF-EXT]. One major challenge associated with such label advertisement mechanism is how to avoid a given global MPLS label from being allocated by different routers to different prefixes. Although manual allocation can address such label allocation collision problem, it is error-prone and therefore may not be suitable for large SR network environments. This document proposes an alternative approach for advertising global labels without any 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 January 11, 2014. Xu, et al. Expires January 11, 2014 [Page 1] Internet-Draft Advertising Global Labels Using IGP July 2013 Copyright Notice Copyright (c) 2013 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. 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 [RFC2119]. Table of Contents 1. Introduction ................................................ 3 2. Terminology ................................................. 3 3. Advertising Label Bindings for Prefixes ..................... 3 3.1. Extension to ISIS ...................................... 3 3.2. Extension to OSPFv2 .................................... 4 3.3. Extension to OSPFv3 .................................... 6 4. Requesting Label Bindings for Prefixes ...................... 6 4.1. Extension to ISIS ...................................... 6 4.2. Extension to OSPFv2 .................................... 7 4.3. Extension to OSPFv3 .................................... 7 5. Mapping Server Redundancy and Election ...................... 7 5.1. Extension to ISIS ...................................... 8 5.2. Extension to OSPFv2 .................................... 8 5.3. Extension to OSPFv3 .................................... 8 6. Security Considerations ..................................... 9 7. IANA Considerations ......................................... 9 8. Acknowledgements ............................................ 9 9. References .................................................. 9 9.1. Normative References ................................... 9 9.2. Informative References ................................. 9 Authors' Addresses ............................................ 10 Xu, et al. Expires January 11, 2014 [Page 2] Internet-Draft Advertising Global Labels Using IGP July 2013 1. Introduction Segment Routing (SR) [SR-ARCH] is a new MPLS paradigm in which each SR-capable router is required to independently advertise global MPLS labels for its attached prefixes using IGP [SR-ISIS-EXT][SR-OSPF-EXT]. One major challenge associated with such label advertisement mechanism is how to avoid a given global MPLS label from being allocated by different routers to different prefixes. Although manual allocation can address such label allocation collision problem, it is error-prone therefore may not be suitable for large SR network environments. This document proposes an alternative approach for advertising global labels without any risk of label allocation collision. The basic idea of this approach is that a single mapping server would, on behalf of all SR-capable routers within an IGP domain, allocate global labels for prefixes attached to those SR-capable routers and then advertise the label bindings in the IGP domain scope. Those prefixes which need to be allocated with global labels can be manually configured on the mapping servers or be advertised by the corresponding SR-capable routers to which those prefixes are attached. In the multi-area/level scenario where route summary between areas/levels is required, the IP longest-match algorithm SHOULD be used by SR-capable routers when processing label bindings advertised by the mapping server. As for the scenario where the scope of label advertisement is set to area/level-scoped, it will be discussed in a future version of this document. 2. Terminology This memo makes use of the terms defined in [RFC1195] [RFC2328] [SR- ARCH]. 3. Advertising Label Bindings for Prefixes 3.1. Extension to ISIS A mapping server could uses one or more of the following TLVs to advertise global labels for those prefixes which need to be allocated with global labels: TLV-135 (IPv4) [RFC5305] TLV-235 (MT-IPv4) [RFC5120] Xu, et al. Expires January 11, 2014 [Page 3] Internet-Draft Advertising Global Labels Using IGP July 2013 TLV-236 (IPv6) [RFC5308] TLV-237 (MT-IPv6) [RFC5120] A Label Binding Sub-TLV (TBD) as shown below is associated with a prefix which is contained in one of the above TLVs: 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 4 of this document) for that prefix is received by the mapping server. MPLS Label: a global label for the prefix which is carried in the TLV containing this sub-TLV. Since the mapping server uses these TLVs for label binding advertisement purpose other than building the normal IP routing table, the Metric field MUST be set to a value larger than MAX_PATH_METRIC (i.e., 0xFE000000). 3.2. Extension to OSPFv2 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 Xu, et al. Expires January 11, 2014 [Page 4] Internet-Draft Advertising Global Labels Using IGP July 2013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=TBD | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | Prefix-Len | Sub-TLV-Len | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Prefix (0-4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Sub-TLVs (Variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ? | MT-ID | Prefix-Len | Sub-TLV-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). Sub-TLV-Len: the length of Sub-TLVs. 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. Xu, et al. Expires January 11, 2014 [Page 5] Internet-Draft Advertising Global Labels Using IGP July 2013 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 4 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. 3.3. Extension to OSPFv3 TBD. 4. Requesting Label Bindings for Prefixes 4.1. Extension to ISIS When advertising IP reachability information by using one of the Extended IP Reachability TLVs (i.e., TLV-135, TLV-235, TLV-236 and TLV-237), SR-capable ISIS routers SHOULD mark those among their attached prefixes which need to be allocated with a global label by associating each of these prefixes with a Label Request sub-TLV (type code=TBD) as shown below. 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. In the multi-level scenario where route summary between levels is required, separate Extended IP Reachability TLVs other than those for IP reachability advertisement purpose SHOULD be used for label binding advertisement purpose. Since these separate TLVs are not used for the purpose of building the normal IP routing table, the Metric field MUST be set to a value larger than MAX_PATH_METRIC (i.e., 0xFE000000). Xu, et al. Expires January 11, 2014 [Page 6] Internet-Draft Advertising Global Labels Using IGP July 2013 4.2. Extension to OSPFv2 SR-capable OSPF routers could use one or more Prefix Opaque LSAs as defined in section 3.2 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. 4.3. Extension to OSPFv3 TBD. 5. Mapping Server Redundancy and Election 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 IS-IS or 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 for prefixes on behalf of SR-capable routers. The comparison of Router ID of ISIS or OSPF routers breaks the tie between two or more candidates with the same highest priority. Meanwhile, the one with the second highest priority SHOULD be elected as a backup mapping server. This backup mapping server is responsible for advertising the same label bindings as those advertised by the primary mapping server. In this way, it's possible to avoid unnecessary changes to the data plane (i.e., MPLS forwarding table) of SR-capable routers in the event of mapping server failover. Xu, et al. Expires January 11, 2014 [Page 7] Internet-Draft Advertising Global Labels Using IGP July 2013 5.1. Extension to ISIS Each candidate mapping server SHOULD advertise its capability of being a mapping server and the corresponding priority for mapping server election by attaching a Mapping Server Capability Sub-TLV (type code=TBD) shown as below to an IS-IS Router Capability TLV [RFC4971] with the S flag set (with domain-wide flooding scope). 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. 5.2. Extension to OSPFv2 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. 5.3. Extension to OSPFv3 TBD. Xu, et al. Expires January 11, 2014 [Page 8] Internet-Draft Advertising Global Labels Using IGP July 2013 6. Security Considerations TBD. 7. IANA Considerations TBD. 8. Acknowledgements Thanks to. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 9.2. Informative References [SR-ARCH] 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-00 (work in progress), June 2013. [SR-ISIS-EXT] Previdi, S., Filsfils, C., and A. Bashandy, "IS-IS Segment Routing Extensions", May 2013. [SR-OSPF-EXT] Psenak, P. and S. Previdi, "OSPF Segment Routing Extensions", May 2013. [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, October 2008. [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, October 2008. [RFC4971] Vasseur, J-P., Ed., Shen, N., Ed., and R. Aggarwal, Ed., "Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information", RFC 4971, July 2007. Xu, et al. Expires January 11, 2014 [Page 9] Internet-Draft Advertising Global Labels Using IGP July 2013 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, February 2008. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008. [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, July 2008. [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, July 2007. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, June 2007. Authors' Addresses Xiaohu Xu Huawei Technologies, Beijing, China Phone: +86-10-60610041 Email: xuxiaohu@huawei.com Mach(Guoyi) Chen Huawei Technologies, Beijing, China Phone: +86-10-60610041 Email: mach.chen@huawei.com