Router with 2 (or more) interfaces in same network
Richard A Steenbergen
ras at e-gerbil.net
Tue Nov 11 15:34:31 UTC 2003
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,
> > 22.214.171.124/16 and 126.96.36.199/16. 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 at e-gerbil.net> http://www.e-gerbil.net/ras
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