Network Working Group A. Lindem
Internet-Draft Redback Networks
Intended status: Standards Track A. Roy
Expires: March 12, 2008 Cisco Systems
S. Mirtorabi
Force10 Networks
September 9, 2007
OSPF Multi-Instance Extensions
draft-acee-ospf-multi-instance-00.txt
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Copyright (C) The IETF Trust (2007).
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Internet-Draft OSPF Multi-Instance Extensions September 2007
Abstract
OSPFv3 includes a mechanism for supporting multiple instances on the
same link. OSPFv2 could benefit from such a mechanism in order to
support multiple routing domains on the same subnet. The OSPFv2
instance ID is reserved for support of separate OSPFv2 protocol
instances. This is different from OSPFv3 where it could be used for
other purposes such as putting the same link in multiple areas.
OSPFv2 supports this capability using a separate subnet or the OSPF
multi-area adjacency capability.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. OSPFv2 Instance Packet Encoding . . . . . . . . . . . . . . . 4
3. OSPF Interface Instance ID . . . . . . . . . . . . . . . . . . 6
3.1. Sending and Receiving OSPF packets . . . . . . . . . . . . 6
4. Backward Compatibility and Deployment Considerations . . . . . 7
4.1. Separate Multicast Addresses for Backward Compatibility . 7
4.2. Separate Protocol ID for Backward Compatibility . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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1. Introduction
OSPFv3 [OSPFV3] includes a mechanism for supporting multiple
instances on the same link. OSPFv2 [OSPFV2] could benefit from such
a mechanism in order to support multiple routing domains on the same
subnet. The OSPFv2 instance ID is reserved for support of separate
OSPFv2 protocol instances. This is different from OSPFv3 where it
could be used for other purposes such as putting the same link in
multiple areas. OSPFv2 supports this capability using a separate
subnet or the OSPF multi-area adjacency capability [MULTI-AREA].
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. OSPFv2 Instance Packet Encoding
OSPFv2 currently doesn't offer a mechanism to differentiate packets
for different instances sent and received on the same interface. In
support of this capability, this document introduces a modified
packet header format when the Authentication Type field is split into
an instance ID and type.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version # | Type | Packet length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Instance ID | AuType |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The OSPFv2 Packet Header
Version #
The OSPFv2 version number - 2
Type
The OSPFv2 packet type as specified [OSPFV2].
Packet length
The length of the OSPF protocol packet in bytes. This length
includes the standard OSPF header.
Router ID
The Router ID of the packet's source.
Area ID
A 32-bit number identifying the area corresponding the packet as
specified in [OSPFV2].
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Checksum
OSPFv2 standard checksum calculation as specified in specified in
[OSPFV2].
Instance ID
Enables multiple instances of OSPF to be run over a single link.
Each protocol instance would be assigned a separate Instance ID;
the Instance ID has local subnet significance only. Received
packets whose Instance ID is not equal to the receiving
interface's Instance ID are discarded.
AuType
OSPFv2 authentication type as specified in specified in [OSPFV2].
Authentication
A 64-bit field for Authentication type dependent authentication
data.
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3. OSPF Interface Instance ID
OSPF [OSPFV2] describes the conceptual interface data structure in
section 9. The OSPF Interface ID will be added to this structure.
The Interface Instance ID will default to 0. Its setting to a non-
zero value may be accomplished through configuration or implied by
some usage beyond the scope of this document.
3.1. Sending and Receiving OSPF packets
When sending OSPF packets, if the interface instance ID has a non-
zero value, it will be set in the OSPF packet header. When receiving
OSPF packets, the OSPFv2 Header Instance ID will be used to aid in
demultiplexing the packet and routing it to the correct OSPFv2
instance.
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4. Backward Compatibility and Deployment Considerations
When there are OSPF routers that support this capability on the same
broadcast capable link as those that do not, packets with non-zero
Instance IDs will be received by those legacy routers. Since the
authentication type will be unknown to them they will not process the
packet. This is what is desired. However, the impact varies by
implementation and some implementations may log every single
authentication type mismatch.
4.1. Separate Multicast Addresses for Backward Compatibility
Another way to avoid the backward compatibility problem would be to
use new IPv4 multicast addresses for OSPF multicast packets with non-
zero instance IDs. We would need to reserve two, one for
AllSPFRouters and another for ALLDRouters. This would have the added
benefit that the OSPF routers not supporting this specification would
not receive the packet or at least drop it silently at an earlier
junction. However, it isn't clear whether this is justified simply
for migration.
4.2. Separate Protocol ID for Backward Compatibility
Another way to avoid the backward compatibility problem would be to
use a different IPv4 header protocol ID for OSPF packets with non-
zero instance IDs. This approach would have the added benefit of
allowing all packets associated with a non-zero Instance ID to be
identified at the IP layer. This may be desirable for some
applications utilizing multiple instances.
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5. Security Considerations
The enhancement described herein doesn't add any additional security
considerations to OSPFv2. Security considerations for OSPFv2 are
described in [OSPFV2].
Given that only three OSPFv2 authentication types have been
standardized, it seems reasonable to reduce the OSPF packet header
field to 8 bits.
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6. IANA Considerations
A new registry will be added for OSPF Instance IDs. The allocation
is TBD.
Dependent on the approach, two new multicast addresses from the IPv4
Multicast Addresses registry would need to be allocated.
Dependent on the approach, a new protocol ID may need to be allocated
from the Protocol Numbers registry.
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7. Normative References
[MULTI-AREA]
Mirtorabi, S., Psenak, P., Lindem, A., and A. Oswal, "OSPF
Multi-Area Adjacency",
draft-ietf-ospf-multi-area-adj-08.txt (work in progress).
[OSPFV2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, April 2007.
[RFC-KEYWORDS]
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
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
Force10 Networks
350 Holger Way
San Jose, CA 95134
USA
Email: sina@force10networks.com
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