RE: Getting a "portable" /19 or /20

From: Patrick Evans []
Sent: Tuesday, April 10, 2001 10:22 AM

On the flipside, who is actually less concerned about routing table
size? The multihomed networks on the edges who can use a default if
they want to, and are likely to be carrying less traffic and so have
more resources to deal with routing, or the core networks who have
capacity problems of their own?

AFAICT, multi-homing doesn't work unless you also have dynamic routing. Is
this wrong?

Well, if all you care about is redundant routes (not optimizing paths) and
don't worry about asymmetric paths, you can announce just your prefixes to
each upstream and use only default routes (either received via BGP or
static interface routes) for outbound traffic.

John A. Tamplin
770/436-5387 HOME 4116 Manson Ave
770/431-9459 FAX Smyrna, GA 30082-3723

"announce" presupposes dynamic routing, doesn't it?

You can multi-home with everything routed statically, as long as you
have unsophisiticated requirements for choosing an outbound path, don't
need transport session stability, and can cope with some of your
addresses being unreachable from the rest of the network when one of
your providers stops being able to reach you.

Doing things this way can also make network problems harder to debug.

I multi-home like this at home, between a cheap DSL provider and a
cheap cable-modem supplier. So far there hasn't been a time when
both providers went down simultaneously. I have protected myself
from around forty-eight aggregate hours of downtime over the past
four months, and I haven't had to waste any time on the phone to the
cable operator helpdesk explaining to them the benefits of running
BGP to me.

I could have bought a pair of T1s to different providers and run
BGP; however, this would probably cost me around $3000 per month
more than I'm currently paying, would give me half the performance,
and would require me to buy a router with WAN interfaces (instead
of the OpenBSD box with 3 x $10 NICs).

Oh, and my multi-homing doesn't contribute to state bloat in the DFZ :slight_smile: