[c-nsp] ISIS Route Flapping Issue

[David Jacobs]

Hello All,
So I just encountered a very strange issue and I was trying to get some more
information or opinions on what Just happened.

I am using a Cisco 7507, previously running an RSP16 - 2 GEIP cards and an
OC3 card on a VIP2-50.

On one particular day one of our GEIP cards lost connectivity to one of our
core routers, I used standard troubleshooting techniques IE: change the
cable, change the Gbic reset the card - all of which had no effect. I
replaced the GEIP with a brand new one and I placed it in a different slot,
I still could not get connectivity. As a last ditch effort I reloaded the
router and this is where things get weird.

After the router reload, we started experiencing odd ISIS issues, on all of
our routers we noticed our problem 7507's Loopback address begin to flap

I did a sh ip route X.X.X.X and at times it would say x.x.x.x/32 and other
times I would just see x.x.x.x/16. Quite obviously this made life for my
frame relay customers life misery.
After trying all sorts of steps we could not get the flapping to stop. In a
last ditch effort we offloaded our OC3 onto another router,( we are still
using this router as a lifeboat.)

To skip ahead, I ended up getting a new 7507 chassis, brand new RSP 4 and
brand new GEIP's and OC3 cards. I reconfigured the router with the same Ip
and ISIS config and WHAMMO the same ISIS route flapping begins to happen.
After many hours of troubleshooting one thing I did was change the ISIS NET
address, once this was changed things went back to normal.

Why would changing the NET address suddenly stop an ISIS route from
flapping?

Apologies for the long email, but this problem has been happening for quite
a few weeks now.



Any comments or suggestions would be appreciated

Thanks

DaveJ