Changing the RFC 1583 OSPF compliance setting

In OSPF domains supporting multiple external routes from different areas to the same external destination, multiple AS-external-LSAs advertising the same destination are likely to occur. This can cause routing loops and the network problems that loops typically generate. On the routing switches, if RFC 1583 compatibility is disabled, the preference rules affecting external routes are those stated in RFC-2328, which minimize the possibility of routing loops when AS-external-LSAs for the same destination originate from ASBRs in different areas. However, because all routers in an OSPF domain must support the same routing-loop prevention measures, if the domain includes any routers that support only RFC 1583 preference rules, all routers in the domain must be configured to support RFC 1583.

NOTE: The routing switch is configured, by default, to be compliant with the RFC 1583 OSPF V2 specification. (Use show ip ospf general to view the current RFC 1583 configuration setting.)

All routes in an AS should be configured with the same compliance setting for preference rules affecting external routes. Thus, if any routers in an OSPF domain support only RFC 1583, all routers must be configured with 1583 compatibility. In the default OSPF configuration, RFC 1583 support is enabled for the routing switches.

If all routers in the domain supportRFC 2178 or RFC 2328, you should disable RFC 1583 compatibility on all of the routers, because conformance to these later RFCs provides more robust protection against routing loops on external routes.

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