[c-nsp] BGP Multihomed Selective/Conditional Advertisement

[Nathan]

2008/10/24  <tkacprzynski at spencerstuart.com>:
>
> 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.

I would:

-- forget about conditionals

-- advertise three routes to Cogent. My whole network, with a lot of
prepends, and the two halves of my network, without prepends but with
a community saying "don't export".

-- receive from Cogent their networks (the VPN things you want) and
default. If necessary receive full routes and filter out non-default
non-Cogent routes. Set local preference lower than default on default
route from Cogent, and local-preference higher than default on Cogent
routes.

-- advertise whole network to ATT, without prepends.

-- receive default route from ATT, with default local-preference.

If I've correctly understood what you want then that should do it.

-- 
HTH,
Nathan