From: Kyaw Khine (kkhine@xxxxxxxxxxxx)
Date: Fri Jun 28 2002 - 18:21:12 GMT-3
On either R2 or R3,
router ospf 1
summary-address 10.1.0.0 255.255.0.0 not-advertise
Not-advertise option will turn of P-Bit and hence Type-7 to Type-5 will not
take place on ABR.
See ..
http://www.cisco.com/warp/public/104/nssa.html#2c
Correct me if I'm wrong .
Cheers ...
-----Original Message-----
From: Peter Whittle [mailto:peter@whittle-systems.demon.co.uk]
Sent: Friday, June 28, 2002 4:11 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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