[c-nsp] BGP Multihomed Selective/Conditional Advertisement

[Ben Steele]

If it's purely just for failover (ie you don't want to get billed for
traffic down your failover link while your active is up) then why not just
send the community:

"174:70 70 Set customer route local preference to 70"  

This will make them use ATT's path until the ATT link goes down.

Ben

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
tkacprzynski at SpencerStuart.com
Sent: Saturday, 25 October 2008 9:48 AM
To: avayner at cisco.com; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP Multihomed Selective/Conditional Advertisement


Arie,
Thank you for your response. In my situation, where everything is normal, I
am actually sending their specific communities for them not to advertise my
route to their peers. My only problem is how to change that automatically
when my default route from ATT goes away (ATT circuit does down and I'm in a
failover situation)?

Thank you,



-----Original Message-----
From: Arie Vayner (avayner) [mailto:avayner at cisco.com]
Sent: Fri 10/24/2008 6:03 PM
To: Kacprzynski, Tomasz; cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] BGP Multihomed Selective/Conditional Advertisement
 
Tom,

Instead of not advertising a certain prefix, there is another alternative
using BGP communities which are recognized by your upstream providers.

Take a look for what Cogent supports for example (better ask them for the
official list...):
http://www.onesc.net/communities/as174/

You could play with the local pref communities or the no-export ones

Its not the full answer, but just another idea... Let me know if you are
still stuck...

Arie 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
tkacprzynski at spencerstuart.com
Sent: Friday, October 24, 2008 23:07 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] BGP Multihomed Selective/Conditional Advertisement

 
I have been trying to figure out how to do this and maybe someone will be
able to help me out.
 
I have two ISP connections ISP ATT and ISP Cogent. 
 
(ISP Cogent)    (ISP ATT)
     |                       |
  RO ------------------- R1
 
 
ATT would be used for primarily internet and access to our webservers.
 
Cogent would be primarily used to access Cognet's network that use VPN for
incoming connections only. I do not want to have other networks besides
Cogent's network using this path to access our webserver.
 
I would like to have each other act as a backup for one another. For
instance if ATT fails I want everyone on the internet use Cogent to access
me. If Cogent fails I want everyone on the internet and the VPN connections
on Cogent's network to use ATT.
 
So basically what I was thinking to setup is to accept a default router from
ATT and Cogent. Lower the local preference of Cogent and that way I would
accomplish using ATT as primary internet access.
 
The tricky part is with Cogent and using then to only access their local
networks. Looking through communities I found out Cogent's communities that
would not export my route to their peers and keep it internal within their
AS. This works fine but the problem now is how do I failover if ATT fails?
How do I automatically change my not-export community I'm sending to Cogent
to start adverting the route to its peers?
 
I looked at conditional advertisement, I was able to basically send the
route map with not-export communities to Cogent if the default route from
ATT is present. The problem with this is that once the default router
disappears it doesn't advertise anything to Cogent, none of my routes are
advertised to Cogent.
 
I'm not sure if I could do this sort of a double condition such as 
 
if ATT's default route is present send out to Cogent a route map with
prefixes to not-export my routes if ATT's default route is not present sent
to Cogent a route map without any communities on my routes
 
Basically I'm trying to figure out how I can have multihoming, but with the
constrains that I want 1 ISP to be used for internet and the other to only
access their AS, but still have the capability to automatically failover in
case one of the circuits dies.
 
Thank you for any input or help.
 
 
Tom Kacprzynski
Network Engineer
 
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