On 8/22/2012 4:51 PM, Doug McIntyre wrote:
> On Wed, Aug 22, 2012 at 02:47:21PM -0500, Justin Krejci wrote:
>
>> While I agree with the general sentiment that the IP change and switch
>> change will likely be smooth, the IP change can be done more
>> transparently and has literally nothing to do with the L2 gear.
>> To that end, I don't see any reason to not configure/assign the new IP
>> block now and let folks start using it right away, even before the
>> switch switch.
>>
> But, we don't have a central router?
>
> If your border to the exchange right now got a prefix with the next
> hop of 206.108.255.3, how'd you get there? You'd have no route to host
> for 206.108.255.3.
>
> That is why I brought up the secondary IPs. Once everybody puts in a
> secondary IP in 206.108.255.0/24, they'll know how to try to get to
> 206.108.255.3 for my prefix announcement. But I can't really do the
> prefix announcement with the next-hop in 206.108.255.3 until everybody
> knows how to get to 206.108.255.0/24?
>
>
We can remotely verify that everyone has configured a secondary IP, but
that's just the start. You've also got to duplicate ALL of your peer
BGP sessions beforehand as well. Why? Well,
I don't believe Cisco can initiate a BGP session on a secondary address
so once a $C router switches their primary and secondary, they cannot
initiate a BGP session. Not a problem yet. What about when the next
one does it? Suddenly neither of the Cisco devices can peer with each
other.. I've not been through an exchange re-address, but given this
limitation, I foresee many problems and the idea of a "flag day" much
more appealing - luckily though, most participants are using the route
server.
Hmm... I assume the BIRD configuration allows you to specify source IP's
to be used for each peer?
-James
CDW
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