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Versions: 00 01 02 03 draft-ietf-ospf-transport-instance

Network Working Group                                          A. Lindem
Internet-Draft                                          Redback Networks
Intended status: Standards Track                                  A. Roy
Expires: August 30, 2009                                    S. Mirtorabi
                                                           Cisco Systems
                                                       February 26, 2009


                   OSPF Transport Instance Extensions
               draft-acee-ospf-transport-instance-03.txt

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Abstract

   OSPFv2 and OSPFv3 include a reliable flooding mechanism to
   disseminate routing topology and Traffic Engineering (TE) information
   within a routing domain.  Given the effectiveness of these
   mechanisms, it is convenient to envision using the same mechanism for
   dissemination of other types of information within the domain.
   However, burdening OSPF with this additional information will impact
   intra-domain routing convergence and possibly jeopardize the
   stability of the OSPF routing domain.  This document presents
   mechanism to relegate this ancillary information to a separate OSPF
   instance and minimize the impact.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements notation  . . . . . . . . . . . . . . . . . .  3
   2.  OSPF Transport Instance  . . . . . . . . . . . . . . . . . . .  4
     2.1.  OSPFv2 Transport Instance Packets Differentiation  . . . .  4
     2.2.  OSPFv3 Transport Instance Packets Differentiation  . . . .  4
     2.3.  Instance Relationship to Normal OSPF Instances . . . . . .  4
       2.3.1.  Ships in the Night Relationship to Normal OSPF
               Instances  . . . . . . . . . . . . . . . . . . . . . .  4
       2.3.2.  Tigher Coupling with Normal OSPF Instances . . . . . .  5
     2.4.  Network Prioritization . . . . . . . . . . . . . . . . . .  5
     2.5.  OSPF Transport Instance Omission of Routing Calculation  .  5
     2.6.  Non-routing Instance Separation  . . . . . . . . . . . . .  5
     2.7.  Non-Routing Sparse Topologies  . . . . . . . . . . . . . .  6
       2.7.1.  Remote OSPF Neighbor . . . . . . . . . . . . . . . . .  7
   3.  OSPF Transport Instance Information Encoding . . . . . . . . .  8
     3.1.  OSPFv2 Transport Instance Information Encoding . . . . . .  8
     3.2.  OSPFv3 Transport Instance Information Encoding . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13













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1.  Introduction

   OSPFv2 [OSPFV2] and OSPFv3 [OSPFV3] include a reliable flooding
   mechanism to disseminate routing topology and Traffic Engineering
   (TE) information within a routing domain.  Given the effectiveness of
   these mechanisms, it is convenient to envision using the same
   mechanism for dissemination of other types of information within the
   domain.  However, burdening OSPF with this additional information
   will impact intra-domain routing convergence and possibly jeopardize
   the stability of the OSPF routing domain.  This document presents
   mechanism to relegate this ancillary information to a separate OSPF
   instance and minimize the impact.

1.1.  Requirements notation

   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-KEYWORDS].

































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2.  OSPF Transport Instance

   In order to isolate the overhead of flooding non-routing information,
   its flooding will be relegated to a separate protocol instance.  This
   instance should be given lower priority when contending for router
   resources including processing, backplane bandwidth, and line card
   bandwidth.  How that is realized is an implementation issue and is
   beyond the scope of this document.

2.1.  OSPFv2 Transport Instance Packets Differentiation

   OSPFv2 currently doesn't offer a mechanism to differentiate Transport
   instance packets from normal instance packets sent and received on
   the same interface.  However, the [MULTI-INST] provides the necessary
   packet encoding to support multiple OSPF protocol instances.

2.2.  OSPFv3 Transport Instance Packets Differentiation

   Fortunately, OSPFv3 already supports separate instances within the
   packet encodings.  The existing OSPFv3 packet header instance ID
   field will be used to differentiate packets received on the same link
   (refer to section 2.4 in [OSPFV3]).

2.3.  Instance Relationship to Normal OSPF Instances

   There are basically two alternatives for the relationship between a
   normal OSPF instance and a Transport Instance.  In both cases, we
   must guarantee that any information we've received is treated as
   valid if and only if the router sending it is reachable.  We'll refer
   to this as the "condition of reachability" in this document.

   1.  Ships in the Night - The Transport Instance has no relationship
       or dependency on any other OSPF instance.

   2.  Child Instance - The Transport Instance has a child-parent
       relationship with a normal OSPF instance and is dependent on this
       for topology information and assuring the "condition of
       reachability".

2.3.1.  Ships in the Night Relationship to Normal OSPF Instances

   In this mode, the Transport Instance is not dependent on any other
   OSPF instance.  It does, however, have much of the overhead as
   topology information must be advertised to satisfy the condition of
   reachability.

   Prefix information does this need to be advertised.  This implies
   that for OSPFv2, only router-LSAs, network-LSAs, and type 4 summary-



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   LSAs need to be advertised.  In the router-LSAs, the stub (type 3)
   links may be suppressed.  For OSPFv3, this implies that router-LSAs,
   Network-LSAs, and inter-area-router-LSAs must be advertised.

2.3.2.  Tigher Coupling with Normal OSPF Instances

   Further optimization and coupling between the transport instance and
   a normal OSPF instance are beyond the scope of this document.  This
   is an area for future study.

2.4.  Network Prioritization

   While OSPFv2 (section 4.3 in [OSPFV2]) are normally sent with IP
   precedence Internetwork Control, any packets sent by a transport
   instance will be sent with IP precedence Flash (B'011').  This is
   only appropriate given that this is a pretty flashy mechanism.

   Similarly, OSPFv3 transport instance packets will be sent with the
   traffic class mapped to flash (B'011') as specified in ([OSPFV3].

   By setting the IP/IPv6 precedence differently for OSPF transport
   instance packets, normal OSPF routing instances can be given priority
   during both packet transmission and reception.  In fact, Some router
   implemenations map the IP precedence directly to their internal
   packet priority.  However, implementation issues are beyond the scope
   of this document.

2.5.  OSPF Transport Instance Omission of Routing Calculation

   Since the whole point of the transport instance is to separate the
   routing and non-routing processing and fate-sharing, a transport
   instance SHOULD NOT install any routes.  OSPF routers SHOULD NOT
   advertise any transport instance LSAs containing IP or IPv6 prefixes
   and OSPF routers receiving LSAs advertising prefixes SHOULD ignore
   them.  This implies that an OSPFv2 transport instance Link State
   Database should not include any Summary-LSAs (type 3) , AS-External-
   LSAs (type 5), or NSSA-LSAs (type 7) and the Router-LSAs should not
   include any stub (type 3) links.  An OSPFv3 transport instance Link
   State database should not include any Inter-Area-Prefix-LSAs (type
   0x2003), AS-External-LSAs (0x4005), NSSA-LSAs (type 0x2007), or
   Intra-Area-Prefix-LSAs (type 0x2009).  If they are erroneously
   advertised, they MUST be ignored by OSPF routers supporting this
   specification.

2.6.  Non-routing Instance Separation

   It has been suggested that an implementatin could obtain the same
   level of separation between IP routing information and non-routing



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   information in a single instance with slight modifications to the
   OSPF protocol.  The authors refute this contention for the following
   reasons:

   o  Adding internal and external mechanisms to prioritize routing
      information over non-routing information are much more complex
      than simply relegating the non-routing information to a separate
      instance as proposed in this specification.

   o  The instance boundary offers much better separation for allocation
      of finite resources such as buffers, memory, processor cores,
      sockets, and bandwidth.

   o  The instance boundary decreases the level of fate sharing for
      failures.  Each instance may be implemented as a separate process
      or task.

   o  With non-routing information, many times not every router in the
      OSPF routing domain requires knowledge of every piece of routing
      information.  In these cases, groups of routers which need to
      share information can be segregated into sparse topologies greatly
      reducing the amount of non-routing information any single router
      needs to maintain.

2.7.  Non-Routing Sparse Topologies

   With non-routing information, many times not every router in the OSPF
   routing domain requires knowledge of every piece of routing
   information.  In these cases, groups of routers which need to share
   information can be segregated into sparse topologies.  This will
   greatly reduce the amount of information any single router needs to
   maintain with the core routers possibly not requiring any non-routing
   information at all.

   With normal OSPF, every router in an OSPF area must have every piece
   of topological and IP or IPv6 prefix routing information.  With non-
   routing information, only the routers needing to share a set of
   information need be part of the corresponding sparse topology.  For
   directly attached routers, one only need to configure the esired
   topologies on the interfaces with routers requiring the non-routing
   information.  When the routers making up the sparse topology are not
   part of a uniconnected graph, two alternatives exist.  The first
   alternative is configure tunnels to form a fully connected graph
   including only those routers in the sparse topology.  The second
   alternative is use remote neighbors as described in Section 2.7.1.






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2.7.1.  Remote OSPF Neighbor

   With sparse topologies, OSPF routers sharing non-routing information
   may not be directly connected.  OSPF adjacencies with remote
   neighbors are formed exactly as they are with regular OSPF neighbors.
   The main difference is that a remote OSPF neighbor's address is
   configured and IP routing is used to deliver packet to the remote
   neighbor.  Other salient feature of remote neighbor include:

   o  All OSPF packets are addressed to the remote neighbor's configured
      IP address.

   o  The adjacency is represented in the router Router-LSA as a router
      (type-1) link with the link data set to the remote neighbor
      address.

   o  Similar to NBMA networks, a poll-interval is configured to
      determine if the remote neighbor is reachable.  This value is
      normally much higher than the hello interval.
































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3.  OSPF Transport Instance Information Encoding

   The format of the TLVs within the body of an LSA containing non-
   routing information is the same as the format used by the Traffic
   Engineering Extensions to OSPF [TE].  The LSA payload consists of one
   or more nested Type/Length/Value (TLV) triplets.  The format of each
   TLV is:


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


                                TLV Format

   However, each unique application using the mechanisms defined in this
   document will have it's own unique ID.  Whether to encode this ID as
   the top-level TLV or make it part of the OSPF LSA ID is open for
   debate.

   The specific TLVs and sub-TLVs relating to a given application and
   the corresponding IANA considerations MUST for standard applications
   MUST be specified in the document corresponding to that application.

3.1.  OSPFv2 Transport Instance Information Encoding

   Application specific information will be flooded in opaque LSAs as
   specified in [OPAQUE].

3.2.  OSPFv3 Transport Instance Information Encoding

   Application specific information will be flooded in separate LSAs
   with separate function codes.  Refer to section A.4.2.1 of [OSPFV3]
   for information on the LS Type encoding in OSPFv3.












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4.  Security Considerations

   The security considerations for the Transport Instance will not be
   different for those for OSPFv2 [OSPFV2] and OSPFv3 [OSPFV3].















































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5.  IANA Considerations

   No new IANA assignments are required for this draft.
















































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6.  Normative References

   [MULTI-INST]
              Lindem, A., Mirtorabi, S., and A. Roy, "OSPF Multi-
              Instance Extensions",
              draft-acee-ospf-multi-instance-02.txt (work in progress).

   [OPAQUE]   Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, July 2008.

   [OSPFV2]   Moy, J., "OSPF Version 2", RFC 2328, April 1998.

   [OSPFV3]   Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

   [RFC-KEYWORDS]
              Bradner, S., "Key words for use in RFC's to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [TE]       Katz, D., Yeung, D., and K. Kompella, "Traffic Engineering
              Extensions to OSPF", RFC 3630, September 2003.






























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Appendix A.  Acknowledgments

   The RFC text was produced using Marshall Rose's xml2rfc tool.
















































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Authors' Addresses

   Acee Lindem
   Redback Networks
   102 Carric Bend Court
   Cary, NC  27519
   USA

   Email: acee@redback.com


   Abhay Roy
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: akr@cisco.com


   Sina Mirtorabi
   Cisco Systems
   3 West Plumeria Drive
   San Jose, CA  95134
   USA

   Email: sina@cisco.com
























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