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Versions: 00

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.








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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





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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]




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       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



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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           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.





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       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).



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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.




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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.



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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.




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   [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


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