RFC 1583 compatibility

Question: Does RFC 1583 compatibility have impact on route selection? Is RFC 1583 compatibility enabled by default?

Answer: The rfc1583 compatible command is used to enable the routing selection rule compatible with RFC 1583. After the undo rfc1583 compatible command is executed:
If two routes, one in the backbone area and the other in a non-backbone area, direct to the ASBR, the route in the non-backbone area is preferentially selected.
If all routes to the ASBR are in non-backbone areas, the route with the lowest cost is preferentially selected. If the routes have the same cost value, the route with the largest area ID has the highest precedence.
If the routes to the ASBR are in both backbone area and non-backbone areas, the route with the lowest cost is preferentially selected. If the routes have the same cost value, the route with the largest area ID is preferentially selected. The area ID of the backbone area is 0, so that routes in the backbone area will not be selected.
On an S series switch supporting OSPF, RFC 1583 compatibility is enabled by default. If multiple routes exist, the switch selects the route with the lowest cost. If the routes have the same cost value, the switch selects the route with the largest area ID.

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