Loading balancing with more than one ISP.

[Tillman Hodgson]

On Wed, Jan 14, 2004 at 02:46:28PM -0000, Simon Gray wrote:
> > I've been looking for answers on this for a while but I found nothing nor
> > no-one who could tell me if and how it is possible.
> > Let the list know if you find anything interesting.
> 
> Easiest way I would of thought would be to use BGP or OSPF under Zebra
> (/usr/ports/net/zebra)(www.zebra.org)

I'm a heavy Zebra (migrating to Quagga) user. Using dynamic routing is
very handy, but it won't solve the problem of balancing load across two
connections.

Zebra (or any dynamic routing daemon) only makes routing *decisions* and
then places the results of those decisions into the regular kernel
routing table. It doesn't actually route the packets, the regular kernel
routing mechanism still does that.

FreeBSD doesn't allow routes to identical destinations with different
gateways.  For a previous (and recent) thread on this, see
http://lists.freebsd.org/pipermail/freebsd-i386/2003-October/000340.html.

So you can't round-robin between two default gateways. You /can/,
however, send traffic for different destinations out of different links.
For example, I send my nightly CVSup traffic and other automated
downloads out of a regular ADSL link in order to prevent swamping my
main link.

If your upstream providers support dynamic routing protocols, then you
can get that destination information automatically. But that's not the
same as load balancing, it's best-path selection.

-T


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