Hi All, I have one interesting question regarding the behavior of certain routers (including CISCO), when rfc1583Compatibility is enabled. (By default it is disabled).
According to rfc2328, it clearly says in section 16.4, when rfc1583Compatibility is enabled, the preference rules mentioned in 16.4.1 should not be applied in choosing the best path to ASBR. Instead it should select the path based on the cost only i.e whichever path has the lowest cost should be considered as the best path, and if there are multiple low cost paths to ASBR, then choose that path through highest AREA ID, when considered as an unsigned integer. With this background, I tested the behavior of CISCO series 2651 IOS software release 12.4. I was surprised with the CISCO's behavior. Instead of choosing a low cost path when rfc1583compatibility is enabled, it continued to select the path to ASBR based on the preference rules (i.e path through non-backbone intra-area path). I know that rfc2328 uses preference rules specified in 16.4.1 to avoid formation of routing loops, in rfc1583 implementation in certain topologies as explained by Richard Woundy in rfc2178. But still network provider can have a topology where there is no chance of such loops forming, so he may want to use rfc1583 behavior to select the low cost path to ASBR, CISCO doesn't seem to be allowing that. Is there any specific reason why CISCO doesn't allow such behavior, I couldn't immediately find the reason, why CISCO(as well as other implementations like IP Infusion ZebOS) is behaving like this. If there are multiple routers behaving similarly, but not the way rfc2328 has specified, then there must be some reason. Does any one know the reason to this behavior ? regards, Shashidhar _______________________________________________ OSPF mailing list [email protected] https://www1.ietf.org/mailman/listinfo/ospf
