[65083] in North American Network Operators' Group
Re: Router with 2 (or more) interfaces in same network
daemon@ATHENA.MIT.EDU (Richard A Steenbergen)
Tue Nov 11 10:36:51 2003
Date: Tue, 11 Nov 2003 10:34:31 -0500
From: Richard A Steenbergen <ras@e-gerbil.net>
To: nanog@trapdoor.merit.edu
In-Reply-To: <20031111145534.GA47252@ussenterprise.ufp.org>
Errors-To: owner-nanog-outgoing@merit.edu
On Tue, Nov 11, 2003 at 09:55:34AM -0500, Leo Bicknell wrote:
> In a message written on Tue, Nov 11, 2003 at 08:35:34AM +0000, Sugar, Sylvia wrote:
> > I am curious to know if its possible to have a router with its two interfaces, say configured as,
> > 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.
I'm not sure how Cisco is wrong on this one. If you want 2 router
interfaces to have the same route and you actually want both of them to
work, it means at the very least you must have a non point-to-point
medium, such as Ethernet. In this case, the correct configuration would be
a bridge-group and IRB, creating a virtual routed interface with 2
physical ports for bridging.
> 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 love FreeBSD, but it's routing code is probably the thing you least want
to look to for examples on how things should be. BTW there is a netgraph
module for L2 hash-based load balancing (aka etherchannel without the
PAgP/LACP), but yeah the lack of ECMP and a reasonable switching method to
support it falls into the category of the previous sentence. :)
--
Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
