[65080] in North American Network Operators' Group
Re: Router with 2 (or more) interfaces in same network
daemon@ATHENA.MIT.EDU (Leo Bicknell)
Tue Nov 11 09:56:11 2003
Date: Tue, 11 Nov 2003 09:55:34 -0500
From: Leo Bicknell <bicknell@ufp.org>
To: nanog@trapdoor.merit.edu
Mail-Followup-To: nanog@trapdoor.merit.edu
In-Reply-To: <20031111083534.59978.qmail@web25001.mail.ukl.yahoo.com>
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In a message written on Tue, Nov 11, 2003 at 08:35:34AM +0000, Sugar, Sylvi=
a wrote:
> I am curious to know if its possible to have a router with its two interf=
aces, say configured as,=20
> 1.1.1.1/16 and 1.1.1.2/16. Theoretically, i see nothing which can stop a =
router from doing this.
Cisco's don't let you do this. I have always considered that broken,
although I'm sure Cisco thinks it's a feature. Other routers (of
note FreeBSD boxes) do this just fine. In almost all cases I've
seen it done it was for more bandwidth to the box (typically inbound
only, because there are no good tools on Unix boxes to split the
traffic between the outgoing interfaces). I've seen it done a lot in
labs where you have something like this:
client 1 | | client 5
client 2 +----B----+ client 6
client 3 | | client 7
client 4 | | client 8
| |
file-server-router-box
|
Internet
Where all the clients are in one subnet, there are two interfaces,
and the networks are separated (today the left and right groups on
two different switches, I drew the old school picture of thinwire
with a bridge in the middle.
While this will work (with some boxes, again Cisco's won't let you
configure the same subnet on two interfaces), it is at best a hack
that helps in some specific instances. It is quite clearly not good
network design. Maybe they have one of those specific instances
but I'd get a lot more detail and be sure before you offer up this
hack as otherwise you've got a messy config that didn't do what the
customer wanted anyway.
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org
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