[c-nsp] Conditional BGP

[Terry Baranski]

On Sun, Oct 19, 2008 at 04:36:41AM, Hank Nussbacher wrote:
 
> I am curious if anyone else uses conditional BGP as a poor man's DRP?
> 
> Suppose you have site A with 192.168.1.0/24.  The site is
> connected to 2 upstream ISPs and they have a number of 
> servers at site A.  They now create a DRP site (site B), 
> which is also connected to 2 upstream ISPs and they
> create a mirror copy of those servers from site A over at
> site B and assign them the *exact* same IP addresses as at 
> site A.  They have the router at site B do conditional BGP, 
> checking to see if it sees 192.168.1.0/24 from the Internet.
> As soon as it disappears (site A is gone), site B starts
> announcing 192.168.1.0/24 to the Internet and all the DRP
> servers at site B are suddenly active.  Ignoring the syncing 
> of the servers from site B to site A, what is the downside 
> of such a "poor mans' DRP solution?

I've done something similiar, but went with what I perceived to be the
somewhat less complex route of advertising the routes from both places at
all times, but with AS Prepending and such so that Site A was always
preferred when reachable.  

It worked well, and no DNS games required for failover.

-Terry