[eng/rtg][vendor specific] changing loopbacks

Thu Sep 29 20:05:45 UTC 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 ;-)
>
> Neil.
>
>