From: Hunt Lee (ciscoforme3@yahoo.com.au)
Date: Tue Sep 03 2002 - 10:52:03 GMT-3
Good Morning,
I want to clarify / confirming my understanding regarding filtering
routes with distribute-lists... and would appreciated if anyone could
shed some light on this ;)
distribute-list X in - filters routes learned via all incoming
interfaces from going into the routing table
distribute-list X out - filters any external redistributed routes from
other protocols.
Ok... as for OSPF:-
distribute-list X in - will still filters routes from all incoming
interfaces from entering into the routing table. I have read on
Parkhurst (OSPF Command & Reference) saying that this command can
filters "O" & "O IA" route, but not "O E2" routes, yet I have also read
on other books saying that only "O IA" routes can be filtered by this,
so which is correct?
Also, since OSPF uses LSAs, where OSPF neighbors determines routes from
the info in the Link State database, this command won't stop the routes
from going into OSPF Topology database.
distribute-list X in <Serial 0> - same as above, except the filtering
only applied for routes learned via a specific interface.
distribute-list X out - I have read from different books (as well as
CCO regarding this). Dr Parkhurst (OSPF Command & Reference) says that
this command is useless / has no effect on OSPF... yet I have read on
other sources saying this will still work, where ALL different external
protocols will be filtered with the list (e.g. if EIGRP & RIP are both
redistributed into OSPF, then they would both be filtered).
distribute-list X out <rip> - filters only a specific external
redistributed protocol (O E2) from entering into the ASBR's own OSPF
database, hence these external routes will be prevented to be
advertised to the rest of OSPF domain.
... Apart from those, is it true that I should only use the above 4
commands from OSPF ABR or OSPF ASBR??
Is this correct"
H.
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