path: root/doc/rfc/rfc5838.txt

Internet Engineering Task Force (IETF)                    A. Lindem, Ed.
Request for Comments: 5838                                      Ericsson
Category: Standards Track                                   S. Mirtorabi
ISSN: 2070-1721                                                   A. Roy
                                                               M. Barnes
                                                           Cisco Systems
                                                             R. Aggarwal
                                                        Juniper Networks
                                                              April 2010

                 Support of Address Families in OSPFv3

Abstract

   This document describes a mechanism for supporting multiple address
   families (AFs) in OSPFv3 using multiple instances.  It maps an AF to
   an OSPFv3 instance using the Instance ID field in the OSPFv3 packet
   header.  This approach is fairly simple and minimizes extensions to
   OSPFv3 for supporting multiple AFs.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5838.

Copyright Notice

   Copyright (c) 2010 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.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  Design Considerations  . . . . . . . . . . . . . . . . . .  2
     1.2.  Requirements Notation  . . . . . . . . . . . . . . . . . .  3
   2.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Instance ID Values for New AFs . . . . . . . . . . . . . .  3
     2.2.  OSPFv3 Options Changes . . . . . . . . . . . . . . . . . .  4
     2.3.  Advertising Prefixes in AFs Other Than IPv6  . . . . . . .  4
     2.4.  Changes to the Hello Packet Processing . . . . . . . . . .  4
     2.5.  Next-Hop Calculation for IPv4 Unicast and Multicast AFs  .  5
     2.6.  AS-External-LSA and NSSA-LSA Forwarding Address for
           IPv4 Unicast and IPv4 Multicast AFs  . . . . . . . . . . .  5
     2.7.  Database Description Maximum Transmission Unit (MTU)
           Specification for Non-IPv6 AFs . . . . . . . . . . . . . .  6
     2.8.  Operation over Virtual Links . . . . . . . . . . . . . . .  8
   3.  Backward Compatibility . . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 12

1.  Introduction

   OSPFv3 [OSPFV3] has been defined to support the base IPv6 unicast
   address family (AF).  There are requirements to advertise other AFs
   in OSPFv3, including multicast IPv6, unicast IPv4, and multicast
   IPv4.  This document supports these other AFs in OSPFv3 by mapping
   each AF to a separate Instance ID and OSPFv3 instance.

1.1.  Design Considerations

   This section describes the rationale for using the multiple Instance
   ID approach to support multiple address families in OSPFv3.  As
   described earlier, OSPFv3 is designed to support multiple instances.
   Hence, mapping an instance to an address family doesn't introduce any
   new mechanisms to the protocol.  It minimizes the protocol extensions
   required, and it simplifies the implementation.  The presence of a
   separate link state database per address family is also easier to
   debug and operate.  Additionally, it doesn't change the existing
   instance, area, and interface-based configuration model in most
   OSPFv3 implementations.







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1.2.  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].

2.  Protocol Details

   Currently, the entire Instance ID number space is used for IPv6
   unicast.  This specification assigns different Instance ID ranges to
   different AFs in order to support other AFs in OSPFv3.  Each Instance
   ID implies a separate OSPFv3 instance with its own neighbor
   adjacencies, link state database, protocol data structures, and
   shortest path first (SPF) computation.

   Additionally, the current Link State Advertisements (LSAs) defined to
   advertise IPv6 unicast prefixes can be used to advertise prefixes
   from other AFs without modification.

   It should be noted that OSPFv3 runs on top of IPv6 and uses IPv6 link
   local addresses for OSPFv3 control packets.  Therefore, it is
   required that IPv6 be enabled on an OSPFv3 link, although the link
   may not be participating in any IPv6 AFs.

2.1.  Instance ID Values for New AFs

   Instance ID zero is already defined by default for the IPv6 unicast
   AF.  When this specification is used to support multiple AFs, we
   define the following ranges for different AFs.  The first value of
   each range is the default value for the corresponding AF.

      Instance ID # 0    -  # 31     IPv6 unicast AF
      Instance ID # 32   -  # 63     IPv6 multicast AF
      Instance ID # 64   -  # 95     IPv4 unicast AF
      Instance ID # 96   -  # 127    IPv4 multicast AF
      Instance ID # 128  -  # 255    Unassigned

                            OSPFv3 Instance IDs













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2.2.  OSPFv3 Options Changes

   A new AF-bit is added to the OSPFv3 Options field.  The V6-bit is
   only applicable to the IPv6 unicast AF.

                               1                     2
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5  6 7 8  9 0 1 2 3
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+-+-+--+
          | | | | | | | | | | | | | | | |AF|*|*|DC|R|N|x|E|V6|
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+-+-+--+

                           The Options field

                              OSPFv3 Options

   V6-bit
      The V6-bit is used in OSPFv3 to exclude a node from IPv6 unicast
      route calculation but allow it in the SPF calculation for other
      address families.  Since the Instance ID now denotes the AF
      explicitly, this bit is ignored in AFs other than IPv6 unicast.

   AF-bit
      When an OSPFv3 router is supporting AFs as described in this
      specification, it MUST set the AF-bit in the OSPFv3 Options field
      of Hello packets, Database Description packets, and LSAs.

2.3.  Advertising Prefixes in AFs Other Than IPv6

   Each prefix advertised in OSPFv3 has a prefix Length field [OSPFV3].
   This facilitates advertising prefixes of different lengths in
   different AFs.  The existing LSAs defined in OSPFv3 are used for this
   and there is no need to define new LSAs.

   Prefixes that don't conform to the AF of an OSPFv3 instance MUST NOT
   be used in the route computation for that instance.

2.4.  Changes to the Hello Packet Processing

   When an OSPFv3 router does not support this specification and it is
   configured with the corresponding Instance ID, packets could be black
   holed.  This could happen due to misconfiguration or a router
   software downgrade.  Black holing is possible because a router that
   doesn't support this specification can still be included in the SPF
   calculated path as long as it establishes adjacencies using the
   Instance ID corresponding to the AF.  Note that Router-LSAs and
   Network-LSAs are AF independent.





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   In order to avoid the above situation, Hello packet processing is
   changed in order to only establish adjacencies with routers that have
   the AF-bit set in their Options field.

   Receiving Hello packets is specified in section 4.2.2.1 of [OSPFV3].
   The following check is added to Hello packet reception:

   o  When an OSPFv3 router participates in an AF (sets the AF-bit in
      the Options field), it MUST discard Hello packets having the AF-
      bit clear in the Options field.  The only exception is the Base
      IPv6 unicast AF, where this check MUST NOT be done (for backward
      compatibility).

2.5.  Next-Hop Calculation for IPv4 Unicast and Multicast AFs

   OSPFv3 runs on top of IPv6 and uses IPv6 link local addresses for
   OSPFv3 control packets and next-hop calculations.  Although IPv6 link
   local addresses could be used as next hops for IPv4 address families,
   it is desirable to have IPv4 next-hop addresses.  For example, in the
   IPv4 multicast AF, the Protocol Independent Multicast (PIM) [PIM]
   neighbor address and the next-hop address should both be IPv4
   addresses in order for the Reverse Path Forwarding (RPF) lookup to
   work correctly.  Troubleshooting is also easier when the prefix
   address and next-hop address are in the same AF.

   In order to achieve this, the link's IPv4 address will be advertised
   in the "link local address" field of the IPv4 instance's Link-LSA.
   This address is placed in the first 32 bits of the "link local
   address" field and is used for IPv4 next-hop calculations.  The
   remaining bits MUST be set to zero.

   We denote a Direct Interface Address (DIA) as an IPv4 or IPv6 address
   that is both directly reachable via an attached link and has an
   available layer 3 to layer 2 mapping.  Note that there is no explicit
   need for the IPv4 link addresses to be on the same subnet.  An
   implementation SHOULD resolve layer 3 to layer 2 mappings via the
   Address Resolution Protocol (ARP) [ARP] or Neighbor Discovery (ND)
   [ND] for a DIA even if the IPv4 address is not on the same subnet as
   the router's interface IP address.

2.6.  AS-External-LSA and NSSA-LSA Forwarding Address for IPv4 Unicast
      and IPv4 Multicast AFs

   For OSPFv3, this address is an IPv6 host address (128 bits).  If
   included, data traffic for the advertised destination will be
   forwarded to this address.  For IPv4 unicast and IPv4 multicast AFs,
   the Forwarding Address in AS-external-LSAs and NSSA-LSAs MUST encode
   an IPv4 address.  To achieve this, the IPv4 Forwarding Address is



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   advertised by placing it in the first 32 bits of the Forwarding
   Address field in AS-external-LSAs and NSSA-LSAs.  The remaining bits
   MUST be set to zero.

2.7.  Database Description Maximum Transmission Unit (MTU) Specification
      for Non-IPv6 AFs

   For address families other than IPv6, both the MTU for the instance
   address family and the IPv6 MTU used for OSPFv3 maximum packet
   determination MUST be considered.  The MTU in the Database
   Description packet MUST always contain the MTU corresponding to the
   advertised address family.  For example, if the instance corresponds
   to an IPv4 address family, the IPv4 MTU for the interface MUST be
   specified in the interface MTU field.  As specified in Section 10.6
   of [OSPFV2], the Database Description packet will be rejected if the
   MTU is greater than the receiving interface's MTU for the address
   family corresponding to the instance.  This behavior will assure that
   an adjacency is not formed and address family specific routes are not
   installed over a path with conflicting MTUs.

   The value used for OSPFv3 maximum packet size determination MUST also
   be compatible for an adjacency to be established.  Since only a
   single MTU field is specified, the M6-bit is defined by this
   specification.  If the M6-bit is clear, the specified MTU SHOULD also
   be checked against the IPv6 MTU, and the Database Description packet
   SHOULD be rejected if the MTU is larger than the receiving
   interface's IPv6 MTU.  An OSPFv3 router SHOULD NOT set the M6-bit if
   its IPv6 MTU and address family specific MTU are the same.

   If the IPv6 and IPv4 MTUs differ, the M6-bit MUST be set for non-IPv6
   address families.  If the M6-bit is set, the IPv6 MTU is dictated by
   the presence or absence of an IPv6 MTU TLV in the link-local
   signaling (LLS) [LLS] block.  If this TLV is present, it carries the
   IPv6 MTU that SHOULD be compared with the local IPv6 MTU.  If this
   TLV is absent, the minimum IPv6 MTU of 1280 octets SHOULD be used for
   the comparison (refer to [IPV6]).

   If the M6-bit is set in a received Database Description packet for a
   non-IPv6 address family, the receiving router MUST NOT check the
   Interface MTU in the Database Description packet against the
   receiving interface's IPv6 MTU.










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   The figure below graphically depicts the changed fields in octets
   20-23 of the OSPFv3 Database Description packet:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |        Interface MTU          |      0        |0|0|0|M6|0|I|M|MS|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+

                OSPFv3 Database Description Packet Changes

   The changed fields in the Database Description packet are described
   below.  The remaining fields are unchanged from [OSPFV3].

   Interface MTU
      The size in octets of the largest address family specific datagram
      that can be sent on the associated interface without
      fragmentation.  The MTUs of common Internet link types can be
      found in Table 7-1 of [MTUDISC].  The Interface MTU SHOULD be set
      to 0 in Database Description packets sent over virtual links.

   M6-bit
      The IPv6 MTU bit - this bit indicates that the sender is using a
      different IPv6 MTU than the MTU for the AF.

   An IPv6 MTU TLV can be optionally carried in an LLS block as
   described above.  This TLV carries the IPv6 MTU for the interface.
   The length field of the TLV is set to 4 bytes.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              17               |               4               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           IPv6 MTU                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Format of IPv6 MTU TLV

   Only one instance of the IPv6 MTU TLV MAY appear in the LLS block.
   Instances subsequent to the first are not processed, and the LLS
   inconsistency SHOULD be logged.









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2.8.  Operation over Virtual Links

   OSPFv3 control packets sent over a virtual link are IPv6 packets and
   may traverse multiple hops.  Therefore, there MUST be a global IPv6
   address associated with the virtual link so that OSPFv3 control
   packets are forwarded correctly by the intermediate hops between
   virtual link endpoints.  Although this requirement can be satisfied
   in IPv6 unicast AFs, it will not function in other AFs as there will
   not be a routable global IPv6 address or forwarding path.  Therefore,
   virtual links are not supported in AFs other than IPv6 unicast.

3.  Backward Compatibility

   All modifications to OSPFv3 apply exclusively to the support of
   address families other than the IPv6 unicast AF using multiple OSPFv3
   instances as described in this specification.  These modifications
   are not applicable to IPv6 unicast topologies and do not preclude
   future single instance mechanisms for supporting multiple address
   families.

   In this section, we will define a non-capable OSPFv3 router as one
   not supporting this specification.  When multiple AFs are supported
   as defined herein, each new AF will have a corresponding Instance ID
   and can interoperate with the existing non-capable OSPFv3 routers in
   an IPv6 unicast topology.  Furthermore, when a non-capable OSPFv3
   router uses an Instance ID that is reserved for a given AF, no
   adjacency will be formed with this router since the AF-bit in the
   Options field will be clear in its OSPFv3 Hello packets.  Therefore,
   there are no backward compatibility issues.  AFs can be gradually
   deployed without disturbing OSPFv3 routing domains with non-capable
   OSPFv3 routers.

4.  Security Considerations

   IPsec [IPsec] can be used for OSPFv3 authentication and
   confidentiality as described in [OSPFV3-AUTH].  When multiple OSPFv3
   instances use the same interface, they all MUST use the same Security
   Association (SA), since the SA selectors do not provide selection
   based on data in OSPFv3 Header fields (e.g., the Instance ID).  This
   restriction is documented in Section 8 of [OSPFV3-AUTH].

   Security considerations for OSPFv3 are covered in [OSPFV3].









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5.  IANA Considerations

   The following IANA assignments were made from existing registries.

   o  The AF-bit was assigned from the OSPFv3 Options registry as
      defined in Section 2.2.

   o  The M6-bit was assigned from the DD Packet Flags registry as
      defined in Section 2.7

   o  The TLV type (17) for the IPv6 MTU TLV was assigned from the OSPF
      LLS TLVs registry.

   IANA created a new registry, "OSPFv3 Instance ID Address Family
   Values", for assignment of the mapping of OSPFv3 Instance IDs to
   address families when this specification is used to support multiple
   address families.  Note that the Instance ID field MAY be used for
   applications other than the support of multiple address families.
   However, if it is being used for address families as described in
   this specification, the assignments herein SHOULD be honored.































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            +-------------+----------------------+--------------------+
            | Value/Range | Designation          | Assignment Policy  |
            +-------------+----------------------+--------------------+
            | 0           | Base IPv6 Unicast AF | Already assigned   |
            |             |                      |                    |
            | 1-31        | IPv6 Unicast AFs     | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 32          | Base IPv6 Multicast  | Already assigned   |
            |             |                      |                    |
            | 33-63       | IPv6 Multicast AFs   | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 64          | Base IPv4 Unicast AF | Already assigned   |
            |             |                      |                    |
            | 65-95       | IPv4 Unicast AFs     | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 96          | Base IPv4 Multicast  | Already assigned   |
            |             |                      |                    |
            | 97-127      | IPv4 Multicast AFs   | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 128-255     | Unassigned           | Standards Action   |
            +-------------+----------------------+--------------------+

                 OSPFv3 Address Family Use of Instance IDs

   o  Instance IDs 0-127 are assigned by this specification.

   o  Instance IDs in the range 128-255 are not assigned at this time.
      Before any assignments can be made in this range, there MUST be a
      Standards Track RFC including an IANA Considerations section
      explicitly specifying the AF Instance IDs being assigned.













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6.  References

6.1.  Normative References

   [IPV6]          Deering, S. and R. Hinden, "Internet Protocol,
                   Version 6 (IPv6) Specification", RFC 2460,
                   December 1998.

   [IPsec]         Kent, S. and K. Seo, "Security Architecture for the
                   Internet Protocol", RFC 4301, December 2005.

   [OSPFV2]        Moy, J., "OSPF Version 2", STD 54, RFC 2328,
                   April 1998.

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

   [OSPFV3-AUTH]   Gupta, M. and S. Melam, "Authentication/
                   Confidentiality for OSPFv3", RFC 4552, June 2006.

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

6.2.  Informative References

   [ARP]           Plummer, D., "Ethernet Address Resolution Protocol:
                   Or Converting Network Protocol Addresses to 48.bit
                   Ethernet Address for Transmission on Ethernet
                   Hardware", STD 37, RFC 826, November 1982.

   [LLS]           Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
                   Young, "OSPF Link-Local Signaling", RFC 5613,
                   August 2009.

   [MTUDISC]       Mogul, J. and S. Deering, "Path MTU Discovery",
                   RFC 1191, November 1990.

   [ND]            Narten, T., Nordmark, E., Simpson, W., and H.
                   Soliman, "Neighbor Discovery for IP version 6
                   (IPv6)", RFC 4861, September 2007.

   [PIM]           Fenner, B., Handley, M., Holbrook, H., and I.
                   Kouvelas, "Protocol Independent Multicast - Sparse
                   Mode (PIM-SM): Protocol Specification (Revised)",
                   RFC 4601, August 2006.






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RFC 5838                        OSPFv3 AF                     April 2010


Appendix A.  Acknowledgments

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

   Thanks to Tom Henderson and the folks at Boeing for implementing this
   document in the Quagga routing suite, http:www.quagga.net.

   Thanks to Nischal Sheth for review and comments.

   Thanks to Christian Vogt for comments during the Gen-ART review.

   Thanks to Adrian Farrel for comments during the IESG review.

   Thanks to Alfred Hoenes for comments during the editing process.





































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Authors' Addresses

   Acee Lindem (editor)
   Ericsson
   102 Carric Bend Court
   Cary, NC  27519
   USA

   EMail: acee.lindem@ericsson.com


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

   EMail: smirtora@cisco.com


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

   EMail: akr@cisco.com


   Michael Barnes
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   EMail: mjbarnes@cisco.com


   Rahul Aggarwal
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   USA

   EMail: rahul@juniper.net






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