From: gladston@br.ibm.com
Date: Tue May 24 2005 - 21:08:20 GMT-3
Hi Jeff,
Suppose you are told to configure the routers so BRI is not used if Frame-Relay is
up. It is not allowed to used backup interface.
That is a difficult task, because there is no conditional filter (filter advertisement through ISDN if Frame Relay is up and advertise if Frame Relay is down).
OSPF traditional filters does not help.
One way I played around some time ago was to set the distance based on the router id. It worked fine on 12.2T.
We configure the distance of the same route learned from ISDN to 110.
The route learned from Frame Relay has a small distance, so it is prefered.
On your example, R3 would be configured to change the distance of route learned from R5 to 110. The same route learned from R1 would have the default cost.
====================
R3 ~ISDN~ R5
| /
Frame Frame
| /
R1
The ISDN link is area 13. The R1R3 frame is area 12. The R1R5 frame is
area 0.
The route I am describing is R1 Loopback, which is in area 0. R3 chooses
the high cost ISDN path over the low-cost inter-area R1R3 frame path.
=====================
I did it some time ago, so I will lab it again to be sure I remembered it correctly.
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