From: Frank Jimenez (franjime@xxxxxxxxx)
Date: Fri Jun 28 2002 - 19:30:07 GMT-3
Are we allowed to have two different OSPF processes running? If so, we
can run two different OSPF processes and redistribute between the R2/R3
process and the R3/R4 process.
Frank Jimenez, CCIE #5738
franjime@cisco.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Peter Whittle
Sent: Friday, June 28, 2002 3:11 PM
To: CCIELab Studygroup
Subject: OSPF route filtering teaser
Selectively blocking OSPF routes between areas
----------------------------------------------
I would like to pose a simple scenario to the group.
There are 4 routers R1 .. R4
R1 is injecting routes into RIPv2 say 10.1.0.0/16
R2 is running RIPv2 on e0, it is also connected by e1 to OSPF Area 1 and
must inject the routes learnt from RIP into AREA 1. There are other
routers also connected to the ethernet segment in Area 1 again running
OSPF. The routes injected by R2 into area 1 must be visible to these
routers via OSPF.
R3 has 2 ethernet interfaces e0 in OSPF Area 0, and e1 in OSPF Area 1.
It must see the RIP routes injected into OSPF by R2 (ie 10.1.0.0/16).
R4 in connected to the ethernet in Area 0 and is also running OSPF and
is outside of your control.
STOP the RIP routes that were injected by R2 from being seen in Area 0.
(i.e. block the 10.1.0.0/16 route)
You may only program routers R2, & R3 to achieve this.
Any thoughts, ideas, solutions?
I have one solution in mind but it is not very elegant. I will share
this next week when you have had time to think about the problem.
------------
A distribute-list applied to R3, an ABR, will of course not work. (When
the 10.1 route reaches R3 it is in an LSA. If we apply the distribute-
list x in, it will only block the route going into R3's routing table,
it will not prevent the LSA from being sent on to R4. We are not
permitted to change the other routers in Area 0 so we can not use the
conventional approach of applying the distribute-list x in to each of
the routers in Area 0.
If we apply a distribute-list x out to the ABR it will again have no
impact on the LSA advertising the 10.1 route into Area 0.)
==========================
May enlightenment be yours.
Peter
-- Peter Whittle
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