Network Working Group A. Lindem
Internet-Draft Ericsson
Intended status: Standards Track A. Roy
Expires: March 23, 2012 S. Mirtorabi
Cisco Systems
September 20, 2011
OSPF Multi-Instance Extensions
draft-ietf-ospf-multi-instance-05.txt
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.
Status of this Memo
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This Internet-Draft will expire on March 23, 2012.
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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. State Sharing Optimizations between OSPF instances . . . . . . 7
5. Backward Compatibility and Deployment Considerations . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 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 Interface 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 AuType.
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 with an Instance ID not equal to one of the configured
OSPF Instance IDs on the receiving interface MUST be 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 Instance ID will be added to this
structure. The OSPF 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 OSPF 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. Received packets with an Instance ID not equal to one of
the configured OSPF Instance IDs on the receiving interface MUST be
discarded.
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4. State Sharing Optimizations between OSPF instances
This is beyond the scope of this draft and is an area for further
study.
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5. Backward Compatibility and Deployment Considerations
When there are OSPF routers that support OSPF Multi-Instance
extensions on the same broadcast capable link as OSPF routers that do
not, packets with non-zero OSPF header Instance IDs will be received
by those legacy OSPF routers. Since the authentication type will be
unknown to them they will drop the packet due to an authentication
failure. This is exactly what is expected and desired.
Previously, there was concern that certain implementations would log
every single authentication type mismatch. Additionally, if
ospfIfAuthFailure SNMP trap[OSPF-MIB] generation is enabled, a
separate trap would be generated for each received OSPF packet with a
non-zero Instance ID. However, discussions with implementers have
led us to the conclusion that this is not as severe a problem as we'd
first thought and it will be even less of a problem by the time the
mechanism in this draft is standardized, implemented, and deployed.
Most implementations will dampen both the log entries and the
generation of identical SNMP traps. Hence, the more drastic
mechanisms to avoid legacy OSPF routers from receiving multicast OSPF
packets with non-zero Instance IDs have been removed.
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6. 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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7. IANA Considerations
A new registry will be added for OSPF Instance IDs. The allocation
of OSPF Instance IDs is described below.
+-------------+----------------------+--------------------+
| Value/Range | Designation | Assignment Policy |
+-------------+----------------------+--------------------+
| 0 | Base IPv4 Unicast | Assigned |
| | Instance | |
| | | |
| 1 | Base IPv4 Multicast | Assigned |
| | Instance | |
| | | |
| 2 | Base IPv4 In-band | Assigned |
| | Management Instance | |
| | | |
| 3-127 | Local Policy | Reserved for local |
| | | policy assignment |
| | | |
| 128-255 | Unassigned | Standards Action |
+-------------+----------------------+--------------------+
OSPFv2 Instance ID
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8. Normative References
[MULTI-AREA]
Mirtorabi, S., Psenak, P., Lindem, A., and A. Oswal, "OSPF
Multi-Area Adjacency", RFC 5185, May 2008.
[OSPF-MIB]
Joyal, D., Galecki, P., Giacalone, S., Baker, F., and R.
Coltun, "OSPF Version 2 Management Information Base",
RFC 4750, December 2006.
[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.
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Appendix A. Acknowledgments
The RFC text was produced using Marshall Rose's xml2rfc tool.
Thanks to Paul Wells for commenting on the backward compatibility
issues.
Thanks to Paul Wells and Vladica Stanisic for commenting during the
OSPF WG last call.
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Authors' Addresses
Acee Lindem
Ericsson
102 Carric Bend Court
Cary, NC 27519
USA
Email: acee.lindem@ericsson.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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