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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.

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 .

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 .

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 version number - 2 The OSPFv2 packet type as specified . The length of the OSPF protocol packet in bytes. This length includes the standard OSPF header. The Router ID of the packet's source. A 32-bit number identifying the area corresponding the packet as specified in . OSPFv2 standard checksum calculation as specified in specified in . 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. OSPFv2 authentication type as specified in specified in . A 64-bit field for Authentication type dependent authentication data.

OSPF 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.

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. Received packets with an Instance ID not equal to one of the configured OSPF Instance IDs on the receiving interface MUST be discarded.

This is beyond the scope of this draft and is an area for further study.

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 exactly what is desired. Previously, a concern was that some implementations will log every single authentication type mismatch. However, discussions with implementers have led us to the conclusion that this is not as current 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. Hence, the controversial mechanisms to avoid legacy routers receiving multicast OSPF packets with a non-zero instance ID have been removed.

The enhancement described herein doesn't add any additional security considerations to OSPFv2. Security considerations for OSPFv2 are described in . Given that only three OSPFv2 authentication types have been standardized, it seems reasonable to reduce the OSPF packet header field to 8 bits.

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.

Harvard University Ascend Communications, Inc Acoustra Productionss Juniper Network, Inc Sycamore Systems, Inc Redback Networks Force10 Networks Cisco Systems Redback Networks Redback Networks

The RFC text was produced using Marshall Rose's xml2rfc tool. Thanks to Paul Wells for commenting on the backward compatibility issues.