I'm interested in how Cisco's "distribute in" command
works in OSPF context. It seems that if you specify
the access list and the interface name in OSPF
context, then it lets the LSAs arriving over the
specified interface into the OSPF database (that is,
it doesn't drop them since the database of two
neighbors have to be synchronized), but drops the
routes resulting from those LSAs if the access list
denies such routes.
My first question is does Cisco drop the routes
depending on which interface the LSAs arrived on, or
does it drop the routes if the routes have the same
forwarding interface as the one specifed in the
distribute in command?
My second question is what is the purpose of this
command in OSPF context? It might lead to black holes,
since this router may flood the LSAs to another
neighbor which may install the routes. Now, the
upstream router will forward packets destined for such
routes to the given router which will simply drop
them. ISIS doesn't support this command and it seems
that OSPF also shouldn't do it. What was the reason
for implementing this command?
Shivi Fotedar
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