[c-nsp] BGP Multihomed Selective/Conditional Advertisement

[tkacprzynski at SpencerStuart.com]

Nathan, thanks for this idea. Your idea could work. I just need to find
out if they will accept my 2x /25  routes if I split the /24. 

As for the prepend, how could I deal with peers that might be closer to
Cogent than ATT and not load-balance that traffic based on peer's
peering location?

The usage of Cogent is primarily for point to point VPN backup from
other offices that would be on Cogent's network. Ideally I would like to
keep that link free of internet traffic unless the primary (ATT) link
fails and also not have asymmetric traffic where traffic comes in on the
Cogent circuit and leaves on ATT's circuit because of the default route
match. I'm not sure if that's possible, but that would be my ideal
solution.

Thank you,

Tom


-----Original Message-----
From: Nathan [mailto:have.an.email at gmail.com] 
Sent: Sunday, October 26, 2008 10:08 AM
To: Kacprzynski, Tomasz
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP Multihomed Selective/Conditional Advertisement

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