From: Ben-Shalom, Omer (omer.ben-shalom@xxxxxxxxx)
Date: Wed Nov 14 2001 - 17:56:51 GMT-3
Some remarks below - some is tested in the lab but some I did not have time
to test so please forgive (but comment on) any mistakes.
First: I don't think there is any such thing as an OSPF route table, it does
block importing OSPF information into the (one and only) route table,
therefore it will indeed only affect the local router as it does not change
the LSA's or their distribution.
You could in theory use OSPF database filter
ospf database-filter all out will block all LSA's on an interface
neighbor ip-address database-filter all out will block all LSA's to a
neighbor
I don't think it supports route maps or any other way to be selective about
it.
To be really particular about it you could set up 2 ospf processes on the
same router, have one talk to one domain, one to the other and apply route
maps on the redistribution between them.
The good - metrics are retained
The bad - overhead
the ugly - all routes are probably going to become type 5 LSA (external)
also it being OSPF maybe it will just become inter area (need to check in
the lab).
if your router is an ABR and you want to stop routes getting to the backbone
you could also use something like
area X range net mask not-advertise
I checked and you could specify the EXACT network you want suppressed, as it
is covered by it's (own and same) summary address the network LSA itself is
suppressed, the summary in turn is suppressed by the not-advertise statement
so the route never gets to the backbone
I am not sure about the reverse IE doing area 0 range on an ABR to stop a
route from the backbone to the area X but should work the same I think.
I suspect that if the router doing the filtering is an ASBR you could
similarly control what gets into the backbone area with
summary-address address mask {level-1 | level-1-2 | level-2} prefix mask
[not-advertise]
(where the prefix and mask control the neighbor here) so you summ routes and
then not advertise them (or the summary address) so they effectively
disappear (need to check in the lab)
and last - if your router is an ABR you could also use LSA type 3 filtering
to remove knowledge of routes, a good document on this is
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122
t/122t4/ftabrt3f.htm
Unfortunately this is new feature in 12.2
Hope you find this helpful (and not too filled with mistakes)
Omer.
-----Original Message-----
From: Bill Carter [mailto:bcarter@family-net.net]
Sent: Wed, November 14, 2001 7:16 PM
To: Ccielab@Groupstudy. Com; Rajeev Siddappa
Subject: RE: Distribute-list and OSPF
Distribute-list in prevents routes being learned into the OSPF route table.
The problem is OSPF creates the OSPF database and routes are derived from
the database. You will see on the OSPF router w/ distribute-list in, the
route(s) will not appear. If you then look at an OSPF router behind the
filtering OSPF router, the routes appears.
To prevent routes from being redistributed into OSPF you must use another
method of filtering.
Have fun searching for the answer!!!
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Rajeev Siddappa
Sent: Wednesday, November 14, 2001 10:09 AM
To: ccielab@groupstudy.com
Subject: Distribute-list and OSPF
Can some one explain me how does distribute list work
for OSPF
I understnd that it will not efffect when u use it as
distribute list 1 out interface
but how is it working when I use the same as
distribute list 1 in interface .
Pls forward me if you ahve any documents.
Thanks,
Rajeev.
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