My company just implemented BGP for failover situations and found that it
makes use of both (or more) connections unless one goes down. BGP sends
the traffic through the shortest (network) route to the destination so
even if you are connected to two places on one ISP you will have some
traffic going through each link.
On Fri, 11 Jul 1997 mikech @
> From: "Mark Horn [ Net Ops ]" <mhorn @
> Subject: Re: Two ISP's to one DMZ - final post???
> Date: Fri, 11 Jul 1997 09:59:43 -0400
> To: mikech @
> Cc: pferguso @
com, Firewalls @
> > mikech @
> > >> With regards to prefix announcement filtering, it is true that
> > >> there are several larger ISP's which filter announcements on
> > >> a /19 boundary. This is a political problem, not really a
> > >> technical one.
> > >
> > >Unless they won't change the policy. Then you are up the creek.
> > No you aren't. It just means that you have asymetric routing. Suppose
> > you have this:
> > ISPC
> > / \
> > ISPA ISPB
> > \ /
> > You
> > You're using ISPB's addresses and advertising them to ISPA. Suppose ISPC
> > filter's on /19, and you've get filtered. All that will happen is if you
> > send traffic to ISPC via ISPA, the return traffic will come back in via
> > ISPB. Why? Because ISPB is advertising a less specific block than you
> > are and ISPC will not filter that route.
> Mark, I think you forgot that ISPB is kaput. We were talking about using BGP
> in a failover situation. That's why I said you were up a creek. You may try to
> shoot a packet down a dead interface. Because the route change is so small,
> the ISP may not accept the update.
> > --
> > Mark Horn <mhorn @
> > PGP Public Key available from: http://www.es.net/hypertext/pgp.html
> > PGP KeyID/fingerprt: 00CBA571/32 4E 4E 48 EA C6 74 2E 25 8A 76 E6 04 A1 7F
> ---------------End of Original Message-----------------
> By the Way, are there any other Firewalls that support BGP natively?
> Michael W. Chalkley Tel: +1.770.772.4567
> ZapNet! Inc. Fax: +1.770.475.7640
> Suite 400-120 E-mail: mikech @
> 10945 State Bridge Road mikech @
> Alpharetta, GA 30202 http://www.iproute.com