[c-nsp] Conditional BGP

[Fawcett Simon]

Hi Hank 

It's a good question.

Your approach is good as mentioned by others in the thread, if you
advertise both externally  at the same time.  Private peering agreements
may still prefer the prepended route as it costs them less money.

Hence do not advertise your prefix on the backup path as long as the
backup ebgp peer is advertising the route back to you.

This was done with local pref.

simon

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Hank Nussbacher
Sent: 19 October 2008 09:36
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Conditional BGP

At 09:47 PM 18-10-08 +0500, Masood Ahmad Shah 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?

Regards,
Hank

>A nice book on BGP
>
>Practical BGP
>By Russ White
>
>Regards,
>Masood
>BLOG: http://www.weblogs.com.pk/jahil
>
>
>-----Original Message-----
>From: cisco-nsp-bounces at puck.nether.net
>[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Mark Boolootian
>Sent: Wednesday, September 24, 2008 6:06 AM
>To: brandon at sterling.net
>Cc: cisco-nsp at puck.nether.net
>Subject: Re: [c-nsp] Conditional BGP
>
>
> >  2) View the NANOG presentation archives.  Several come to mind;
I'll try
>to
> >  compile a list of suggestions, or just browse away.
>
>Search the presentation archive for Smith and BGP.  Philip Smith's
>BGP tutorials are outstanding.

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