BGP and aggregation

Mon May 13 04:33:54 UTC 2002

On Sun, 12 May 2002, Stephen J. Wilcox wrote:

> Interesting point there Scott.. we were discussing just that at a recent
> IXP meeting I was at. Theres a number of different ways (well hacks) in
> which you can keep connectivity between two halves of an AS network in the
> event of a split.
>
> Is anyone out there actually doing something either this or similar to
> keep two halves connected in the event of a split.. and have you actually
> run successfully on your backup and maintained a reasonable throughput
> (say 30 or 40Mbs) ? I'd be interested if anyone has a proven technique as
> I want to implement something myself and dont really want to test it by
> pulling the plug on some backbone links and waiting to see what happens!

My answer isn't even to close to your reasonable throughput as the example
is only T1 connected, but I have a site which we are only connected to via
a non-igp path.  Everything is via the internet (well sprint.net usually).

We're announcing a /18 to sprint at our main site, and a /23 at the
"disconnected" site.  The "disconnected" site points default at sprint,
and doesn't take a full routing table.  Basically we have BGP up at the
disconnected site just to announce the /23 with our AS.

With some creative use of cisco routing tools including OSPF, GRE tunnels,
and some creative static routing we maintain decent connectivity between
the two sites.  It works quite well.  In fact, it works well enough that
we're starting to buy circuits at each of our POPs as it is cheaper to buy
circuits from sprint or similar to their internet PoPs than it is to buy
circuits around the state.  In most cases we will still be maintaining
internal connectivity for backup and latency reasons.

- Forrest W. Christian (forrestc at imach.com) AC7DE
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