Network Working Group A. Lindem (Editor)
Internet-Draft Redback Networks
Intended status: Standards Track S. Mirtorabi
Expires: April 3, 2008 Force10 Networks
A. Roy
M. Barnes
Cisco Systems
R. Aggarwal
Juniper Networks
October 2007
Support of address families in OSPFv3
draft-ietf-ospf-af-alt-06.txt
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Copyright (C) The IETF Trust (2007).
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Abstract
This document describes a mechanism for supporting multiple address
families in OSPFv3 using multiple instances. It maps an address
family (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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Design Considerations . . . . . . . . . . . . . . . . . . 3
1.2. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Instance ID values for new AFs . . . . . . . . . . . . . . 4
2.2. OSPFv3 Options and Prefix Options Changes . . . . . . . . 4
2.2.1. OSPFv3 Options . . . . . . . . . . . . . . . . . . . . 4
2.2.2. Prefix Options . . . . . . . . . . . . . . . . . . . . 5
2.3. Advertising Prefixes in new AFs . . . . . . . . . . . . . 5
2.4. Changes to the Hello processing . . . . . . . . . . . . . 6
2.5. Next hop for IPv4 unicast and multicast AFs . . . . . . . 6
2.6. AS External LSA Forwarding Address for IPv4 Unicast
and IPv4 Multicast AFs . . . . . . . . . . . . . . . . . 7
2.7. Operation over Virtual Links . . . . . . . . . . . . . . . 7
3. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
OSPFv3 has been defined to support the base IPv6 unicast Address
Family (AF). There is a requirement 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 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.
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].
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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
LSAs that are defined to advertise IPv6 unicast prefixes can be used
without any modifications to advertise prefixes from other AFs.
It should be noted that OSPFv3 is running on the top of IPv6 and uses
IPv6 link local addresses for OSPFv3 control packets and next hop
calculations. Therefore, it is required that IPv6 be enabled on a
link, although the link may not be participating in the IPv6 unicast
AF.
2.1. Instance ID values for new AFs
Instance ID zero is already defined by default for the IPv6 unicast
AF. We define the following ranges for different AFs. The first
value of each range is considered as 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
2.2. OSPFv3 Options and Prefix Options Changes
A new bit is added to the OSPFv3 options field. A couple of the
option bits are only applicable to the IPv6 unicast AF.
2.2.1. OSPFv3 Options
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|MC| E|V6|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+--+--+--+
The Options field
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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 Instance ID now denotes the AF
explicitly, this bit is ignored in AFs other than IPv6 unicast.
MC-bit
This bit is not used in other AFs introduced in this document.
AF-bit
When a router supports AF, it MUST set this new bit in the OSPFv3
Options field of Hello Packets, DD packets, and LSAs.
2.2.2. Prefix Options
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| | | | | P|* |LA|NU|
+--+--+--+--+--+--+--+--+
Prefix Options
MC-bit
This bit is ignored in AFs other than IPv6 Unicast.
NU-bit
The NU bit MUST be clear in all unicast AFs and it MUST be set in
all multicast AFs.
Note that all bits unused in a given AF MAY be redefined for AF
specific purposes in future specifications.
2.3. Advertising Prefixes in new AFs
Each Prefix defined in OSPFv3 has a prefix length field. This
facilitate advertising prefixes of different lengths in different
AFs. The existing LSAs defined in OSPFv3 are used for this purpose
and there is no need to define new LSAs.
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2.4. Changes to the Hello processing
When a router does not support an AF but it is configured 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 the router which doesn't support the AF
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 and network LSAs are AF independent.
In order to avoid the above situation, hello 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 3.2.2.1 of [OSPFV3].
The following check is added to Hello reception:
o When a router participates in an AF (sets the AF-bit in Options
field) it MUST discard Hello packets having the AF-bit clear in
the Options field. The only exception is IPv6 unicast AF, where
this check MUST NOT be done (for backward compatibility).
2.5. Next hop for IPv4 unicast and multicast AFs
OSPFv3 runs on the 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
IPv4 multicast having the next hop address the same as the Protocol
Independent Multicast (PIM) [PIM] neighbor address (IPv4 address)
makes it easier to determine which upstream neighbor to send a PIM
join when doing a Reverse Path Forwarding (RPF) lookup. It is also
easier for troubleshooting to have a next hop with 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 bit of "link local address"
field and used for IPv4 next hop calculations.
We call direct interface address (DIA) the address that is reachable
directly via the link provided that a layer 3 to layer 2 mapping is
available. 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 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.
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2.6. AS External LSA Forwarding Address for IPv4 Unicast and IPv4
Multicast AFs
For OSPFv3, this address is fully qualified IPv6 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 MUST encode an IPv4
address. To achieve this, the IPv4 Forwarding address is advertised
by placing it in the first 32 bits of the Forwarding address field in
the AS-external-LSAs. The remaining bits MUST be set to zero.
2.7. Operation over Virtual Links
OSPFv3 control packets sent over a virtual link are IPv6 packets and
may traverse multiples hops. Therefore, there must be a global IPv6
address associated with the virtual link so that the control packet
is 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.
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3. Backward Compatibility
In this section, we will define a non-capable OSPFv3 router as one
not supporting this specification. 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 which is
reserved for a given AF, no adjacency will be formed with this router
since the AF-bit in the Options field will not be set in Hello
packets. Therefore, there are no backward compatibility issues. AFs
can be gradually deployed without disturbing networks with non-
capable OSPFv3 routers.
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4. Security Considerations
The function described in this document does not create any new
security issues for the OSPF protocol. Security considerations for
the OSPFv3 are covered in [OSPFV3].
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5. IANA Considerations
The following IANA assignments are to be made from existing
registries:
o An OSPFv3 options bit will be allocated for support of address
families using separate instances.
IANA is requested to create a new registry, "OSPFv3 Instance ID
Address Family Values". for assignment of address families IDs. Note
that the Instance ID MAY be used for applications other than the
support of multiple address families. However, if it is being used
for address families the assignments herein should be honored.
+-------------+----------------------+--------------------+
| 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
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o Instancs 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 IANA Considerations explicitely
specifying the AF Instance IDs being assigned.
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6. References
6.1. Normative References
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
[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., "An Ethernet Address Resolution Protocol",
RFC 826, November 1982.
[ND] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[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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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 in
quagga.
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Authors' Addresses
Acee Lindem
Redback Networks
102 Carric Bend Court
Cary, NC 27519
USA
Email: acee@redback.com
Sina Mirtorabi
Force10 Networks
350 Holger Way
San Jose, CA 95134
USA
Email: sina@force10networks.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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