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IETF RFC 6549
Last modified on Tuesday, March 20th, 2012
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Internet Engineering Task Force (IETF) A. Lindem
Request for Comments: 6549 Ericsson
Updates: 2328 A. Roy
Category: Standards Track S. Mirtorabi
ISSN: 2070-1721 Cisco Systems
March 2012
OSPFv2 Multi-Instance Extensions
 Abstract
OSPFv3 includes a mechanism to support multiple instances of the
protocol running on the same interface. OSPFv2 can utilize such a
mechanism in order to support multiple routing domains on the same
subnet.
This document defines the OSPFv2 Instance ID to enable separate
OSPFv2 protocol instances on the same interface. Unlike OSPFv3 where
the Instance ID can be used for multiple purposes, such as putting
the same interface in multiple areas, the OSPFv2 Instance ID is
reserved for identifying protocol instances.
This document updates RFC 2328.
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/RFC 6549.
Lindem, et al. Standards Track PAGE 1 
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
Copyright Notice
Copyright (c) 2012 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.
Table of Contents
1. Introduction ....................................................2
1.1. Requirements Notation ......................................3
2. OSPFv2 Instance Packet Encoding .................................3
3. OSPFv2 Interface Instance ID ....................................4
3.1. Sending and Receiving OSPFv2 Packets .......................4
3.2. Interface Instance ID Values ...............................4
4. State Sharing Optimizations between OSPFv2 Instances ............5
5. OSPFv2 Authentication Impacts ...................................5
6. Backward Compatibility and Deployment Considerations ............5
7. Security Considerations .........................................6
8. IANA Considerations .............................................6
9. References ......................................................7
9.1. Normative References .......................................7
9.2. Informative References .....................................7
Appendix A. Acknowledgments.... ....................................8
1. Introduction
OSPFv3 [OSPFV3] includes a mechanism to support multiple instances of
a protocol running on the same interface. OSPFv2 [OSPFV2] can
utilize such a mechanism in order to support multiple routing domains
on the same subnet.
This document defines the OSPFv2 Instance ID to enable separate
OSPFv2 protocol instances on the same interface. Unlike OSPFv3 where
the Instance ID can be used for multiple purposes, such as putting
the same interface in multiple areas, the OSPFv2 Instance ID is
reserved for identifying protocol instances.
Lindem, et al. Standards Track PAGE 2
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
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].
2. OSPFv2 Instance Packet Encoding
This document extends OSPFv2 with a mechanism to differentiate
packets for different instances sent and received on the same
interface. In support of this capability, a modified packet header
format with the Authentication Type field 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
All fields are as defined in [OSPFV2] except that the Instance ID
field is new, and the AuType field is reduced to 8 bits from 16 bits
without any change in meaning. The Instance ID field is defined as
follows:
Instance ID
Enables multiple instances of OSPFv2 to be used on a single
interface. 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
Instance IDs corresponding to one of the configured OSPFv2
Instances for the receiving interface MUST be discarded.
Lindem, et al. Standards Track PAGE 3
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
3. OSPFv2 Interface Instance ID
Section 9 of [OSPFV2] describes the conceptual interface data
structure. The OSPFv2 Interface Instance ID is added to this
structure. The OSPFv2 Interface Instance ID has a default value of
0. Setting it to a non-zero value may be accomplished through
configuration.
3.1. Sending and Receiving OSPFv2 Packets
When sending OSPFv2 packets, the OSPFv2 Interface Instance ID is set
in the OSPFv2 packet header. When receiving OSPFv2 packets, the
OSPFv2 Header Instance ID is used to aid in demultiplexing the packet
and associating it with the correct OSPFv2 instance. Received
packets with an Instance ID not equal to one of the configured OSPFv2
Instance IDs on the receiving interface MUST be discarded.
3.2. Interface Instance ID Values
The following OSPFv2 Instance IDs have been defined:
0 Base IPv4 Instance - This is the default IPv4 routing instance
corresponding to default IPv4 unicast routing and the
attendant IPv4 routing table. Use of this Instance ID
provides backward compatibility with the base OSPF
specification [OSPFV2].
1 Base IPv4 Multicast Instance - This IPv4 instance corresponds
to the separate IPv4 routing table used for the Reverse Path
Forwarding (RPF) checking performed on IPv4 multicast traffic.
2 Base IPv4 In-band Management Instance - This IPv4 instance
corresponds to a separate IPv4 routing table used for network
management applications.
3-127 Private Use - These Instance IDs are reserved for definition
and semantics defined by the local network administrator. For
example, separate Interface Instance IDs and their
corresponding OSPFv2 instances could be used to support
independent non-congruent topologies for different classes of
IPv4 unicast traffic. The details of such deployments are
beyond the scope of this document.
The first three Interface Instance IDs are analogous to the topology
IDs defined in [RFC 4915].
Lindem, et al. Standards Track PAGE 4
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
4. State-Sharing Optimizations between OSPFv2 Instances
This is beyond the scope of this document and is an area for further
study.
5. OSPFv2 Authentication Impacts
Now that the AuType OSPFv2 header field has been reduced from 2
octets to 1 octet, OSPFv2 routers not supporting this specification
will fail packet authentication for any instance other than the
default (i.e., the Base IPv4 Unicast Instance). This is solely due
to the difference in field definition as opposed to any explicit
change to OSPFv2 authentication, as described in Appendix D of RFC
2328 [OSPFV2] and RFC 5709 [RFC 5709]. However, this is exactly what
is desired since OSPFv2 routers not supporting this specification
should only support the default instance (refer to Section 6).
6. Backward Compatibility and Deployment Considerations
When there are OSPFv2 routers that support OSPFv2 Multi-Instance
extensions on the same broadcast-capable interface as OSPFv2 routers
that do not, packets with non-zero OSPFv2 header Instance IDs are
received by those legacy OSPFv2 routers. Since the non-zero Instance
ID is included in the AuType by these legacy OSPFv2 routers, it is
misinterpreted as a mismatched authentication type and the packet is
dropped. This is exactly what is expected and desired.
Previously, there was concern that certain implementations would log
every single authentication type mismatch. 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 described herein is standardized,
implemented, and deployed. Most implementations will dampen the
logging of errors. Hence, the more drastic mechanisms to avoid
legacy OSPFv2 routers from receiving multicast OSPFv2 packets with
non-zero Instance IDs have been removed.
If the OSPF MIB as specified in [OSPF-MIB] is implemented, even the
damped generation of the ospfIfAuthFailure or ospfVirtIfAuthFailure
Simple Network Management Protocol (SNMP) notifications would be
undesirable in situations where legacy OSPFv2 routers are deployed on
the same subnet as OSPFv2 routers supporting this specification.
Consequently, it is recommended that implementations that implement
this specification and the OSPF MIB also implement SNMP Notification
filtering as specified in Section 6 of [RFC 3413].
Lindem, et al. Standards Track PAGE 5
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
7. Security Considerations
The enhancement described herein doesn't include 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 OSPFv2 packet header
field to 8 bits.
8. IANA Considerations
The size of the AuType field is reduced from 16 octets to 8 octets.
This changes the OSPF Authentication Codes registry in that the
values 256-65535 are no longer defined and are therefore deprecated.
There is no backward compatibility issue since this range of values
was previously defined as "Reserved and should not be assigned".
A new registry has been created for OSPFv2 Instance IDs. The initial
allocation of OSPFv2 Instance IDs is described below. Refer to
Section 3.2 for more information.
+-------------+----------------------+--------------------+
| 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 | Private Use | Reserved for local |
| | | policy assignment |
| | | |
| 128-255 | Unassigned | Standards Action |
+-------------+----------------------+--------------------+
OSPFv2 Instance ID
Lindem, et al. Standards Track PAGE 6
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
9. References
9.1. Normative References
[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.
[RFC-KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[OSPF-MIB] Joyal, D., Ed., Galecki, P., Ed., Giacalone, S., Ed.,
Coltun, R., and F. Baker, "OSPF Version 2 Management
Information Base", RFC 4750, December 2006.
[RFC 3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, RFC
3413, December 2002.
[RFC 4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC
4915, June 2007.
[RFC 5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, October 2009.
Lindem, et al. Standards Track PAGE 7
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
Appendix A. Acknowledgments
Thanks to Adrian Farrel for reviewing and providing some suggested
improvements during the IESG review.
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.
Thanks to Manav Bhatia for comments and for being the document
shepherd.
Thanks to Magnus Nystrom for comments under the auspices of the
Security Directorate review.
Thanks to Dan Romascanu for comments during the IESG review.
Thanks to Pete McCann for comments under the auspices of the Gen-ART
review.
Lindem, et al. Standards Track PAGE 8
RFC 6549 OSPFv2 Multi-Instance Extensions March 2012
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
Lindem, et al. Standards Track PAGE 9
RFC TOTAL SIZE: 16639 bytes
PUBLICATION DATE: Tuesday, March 20th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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