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 From:  "Mitch \(WebCob\)" <mitch at webcob dot com>
 To:  Hilton at QuarkAV dot com, m0n0wall at lists dot m0n0 dot ch
 Subject:  RE: [m0n0wall] m0n0 hacking questions
 Date:  Thu, 22 Apr 2004 14:46:48 -0700
> -----Original Message-----
> From: Hilton Travis [mailto:Hilton at QuarkAV dot com]
> Sent: Thursday, April 22, 2004 1:22 PM
> To: m0n0wall at lists dot m0n0 dot ch
> Subject: RE: [m0n0wall] m0n0 hacking questions
> Hi Barry,
> Assign the same IPs to both devices.  I know it can be done, however I
> don't know how to achieve this successfully.  I have a mate who has done
> this on a few networks he administers - he uses the same IP on two
> machines for routing reasons, and configures routing tables so that its
> not an issue.  This is not because these clients are short of IPs, tho -
> one in particular owns a /24 and a /30 and uses - in total - two of
> these IPs.  :)
> If you wish, I can speak to him and get him to reply.  Linux, tho, but
> the theory should remain valid regardless of the OS involved.
> - HiltonT

Take a look for heartbeat for linux - part of the HA project - works for
FreeBSD too - basically, both devices can have their own IP, and there is
one or more floaters... the machine which is active issues ARP's for the
floaters. I've done this for FreeBSD routers as well as web servers - works
like a charm - the purists (and I am a closet purist) are looking for
stateful failover - which means that open TCP sockets would be kept alive -
and probably IPSec sessions too - that can be done on OpenBSD using PF and
Carp - pf has been ported to newer FreeBSD 5.X, and I think carp works there
as well - no one I know of has it running on 4.9, which is why no one is
playing with it on Mono yet (at least why I haven't ;-)

No time yet to work on a backport - does this info help?