Network Working Group A. Lindem (Editor)
Internet-Draft S. Mirtorabi
Intended status: Standards Track A. Roy
Expires: April 1, 2007 M. Barnes
Cisco Systems
Q. Vohra
R. Aggarwal
Juniper Networks
September 28, 2006
Support of address families in OSPFv3
draft-ietf-ospf-af-alt-04.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
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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 AF's.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Design Considerations . . . . . . . . . . . . . . . . . . 3
1.2. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Instance ID values for new AF's . . . . . . . . . . . . . 4
2.2. OSPFv3 Options and Prefix Options Chnages . . . . . . . . 4
2.2.1. OSPFv3 Options . . . . . . . . . . . . . . . . . . . . 4
2.2.2. Prefix Options . . . . . . . . . . . . . . . . . . . . 5
2.3. Advertising Prefixes in new AF's . . . . . . . . . . . . . 5
2.4. Changes to the Hello processing . . . . . . . . . . . . . 5
2.5. Next hop for IPv4 unicast and multicast AF's . . . . . . . 6
2.6. Operation over Virtual Links . . . . . . . . . . . . . . . 6
3. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
OSPFv3 has been defined to support IPv6 unicast AF. There is a need
to carry other AFs in OSPFv3 such as multicast IPv6, unicast or
multicast IPv4. This document introduces these other AFs in OSPFv3
by reserving Instance IDs and using one OSPFv3 instance for one AF.
1.1. Design Considerations
This section describes the rationale for adopting the multiple
instance ID approach for supporting 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 new mechanisms in 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 OSPF 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 RFC2119 [RFC2119].
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2. Proposed Solution
Currently the entire Instance ID number space is used for IPv6
unicast. We propose to assign different ranges to different AF's in
order to support other AF's in OSPFv3. Each AF will establish
different adjacency, have different link state database and compute
different shortest path tree. Additionally, the current LSAs that
are defined to carry IPv6 unicast prefix can be used without any
modification in different instances to carry different AF's prefixes.
It should be noted that OSPFv3 is running on the top of IPv6 and uses
IPv6 link local address for OSPFv3 control packet and next hop
calculation. Therefore, it is required that IPv6 be enabled on a
link, although the link may not be participating in IPv6 unicast AF.
2.1. Instance ID values for new AF's
Instance ID zero is already used by default for IPv6 unicast AF. We
define the following ranges for different AF's. 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 Reserved
OSPFv3 Instance IDs
2.2. OSPFv3 Options and Prefix Options Chnages
A new bit is added to the OSPFv3 options field and a couple of the
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
OSPFv3 Options
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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 AF's other than IPv6 unicast.
MC-bit
This bit is not used in other AF's introduced in this document.
AF-bit
When a router supports AF, it MUST set this new bit in the 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 not used in other AF's introduced in this document.
NU-bit
The NU bit must be clear in all unicast AF's and it must be set in
all multicast AF's.
Note that all bits unused in a given AF could be redefined later.
2.3. Advertising Prefixes in new AF's
Each Prefix defined in OSPFv3 has a prefix length field. This
facilitate advertising prefixes of different lengths in different
AF's. The existing LSAs defined in OSPFv3 are used for this purpose
and there is no need to define new LSAs.
2.4. Changes to the Hello processing
When a router does not support an AF but it is configured with an
Instance ID in the same range, packets could be blackholed. This
could happen due to misconfiguration or router downgrade to a
previous code level. Blackholing is possible because the router
which doesn't support the AF can still be included in the SPF
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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 adjacency with the 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 participate 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 (to help backward compatibility).
2.5. Next hop for IPv4 unicast and multicast AF's
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 nexthop address the same as the PIM
neighbor address (IPv4 address) makes it easier to know to which
upstream neighbor to send a PIM join when doing a RPF lookup for a
source. It is also easier for troubleshooting purposes to have a
next hop with the same semantics as the 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 ARP or ND for a DIA even if the IPv4
address is not on the same subnet as the router's interface IP
address.
2.6. 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 VL end
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points. Although this requirement can be satisfied in IPv6 unicast
AF, this will not function in other AFs as there cannot be a multihop
forwarding based on global IPv6 address or such a path may not exist.
Therefore virtual link are not currently supported in other AF's.
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3. Backward Compatibility
Each new AF will have their corresponding Instance ID and can operate
with the existing non-capable routers in IPv6 unicast topology.
Further, when a non-capable router uses an Instance ID which is
reserved for a given AF, since the non-capable router will not have
the AF-bit set in the Hello an adjacency will not be established with
an AF capable router. Therefore, there are no backward compatibility
issues. AF's can be gradually deployed without disturbing networks
with current non-capable 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 OSPFv 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.
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6. Normative References
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2119, March 1997.
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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
Cisco Systems
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
Email: acee@cisco.com
Sina Mirtorabi
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
Email: sina@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
Quaizar Vohra
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: qv@juniper.net
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Rahul Aggarwal
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: rahul@juniper.net
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