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Re: [eng/rtg][vendor specific] changing loopbacks

  • From: Warren Kumari
  • Date: Thu Sep 29 16:08:19 2005

So, on vendor C boxes you might be able to get away from having to do a full reboot to change your OSPF ID by doing a "clear ip ospf process".
If you don't do this, even though you change the loopback address, your router will still keep the old address as the OSPF router ID[1]. You won't actually end up with a route to the old loopback, but it will still be in the OSPF database.
While this is less than optimal, it will still work (note, I don't recommend running your network like this!). It is somewhat disconcerting if you don't know that changing loopback address doesn't automatically change OSPF ID[2] and look in your OSPF database and see addresses that you shouldn't / you retired, etc, especially because most people only page through their OSPF database when they suspect something is odd...

Warren Kumari
[1] As with most things, I am sure that the exact behavior depends upon hardware and software version, phase of moon, flavor of doughnut, etc.
[2] Sure it seem obvious when you thin about it, but most people don't seem to think.

On Sep 29, 2005, at 12:20 PM, Neil J. McRae wrote:

this is my fear.  which is why i asked.  pushing out new
configs (the canonic config is on disk, not the router [0])
and setting a reload of a bunch of routers at time t0 does
not give me warm fuzzies about what the world will be like at
time tn (n > 0).

but i may have to take that path.  i am hoping folk will give
me a magic pill.  after all, any group with such a deep
understanding of how to deal with the world's social ills
must know a bit of router magic <smirk>.

I think with OSPF this will be very difficult to
do without rebooting (or as long an outage as rebooting).
We migrated from OSPF to IS-IS and changed some loopbacks a
while ago, the IS-IS change was totally transparent - no issue,
but on the change of loopback caused a lot of BGP churn.
It was easier to change it and reboot and do
it over a period of time in small network triangles.

I always thought that the billing system was the database
of record ;-)


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