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Why is distribute-list in not supported in OSPF? [7:62247] posted 01/31/2003
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Hello,

The "distribute-list access-list in [interface]" command is not supported in
IS-IS and OSPF. Why???

I tried to find an explanation in Cisco's OSPF design guide:

....Filtering information with link-state protocols such as OSPF is a tricky
business. Distribute-list out works on the ASBR to filter redistributed
routes
into other protocols. Distribute-list in works on any router to prevent
routes
from being put in the routing table, but it does not prevent link-state
packets from being propagated, downstream routers would still have the
routes.
It is better to avoid OSPF filtering as much as possible if filters can be
applied on the other protocols to prevent loops....

Why can router not prevent link-state packets from being propagated???

Hope someone can explain this to me. Thanks,

Eric




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