Router with 2 (or more) interfaces in same network

Peter John Hill phill at
Tue Nov 11 14:31:53 UTC 2003

--On Tuesday, November 11, 2003 11:19 AM -0300 Lucas Iglesias <l.iglesias at> wrote:

> As I know, according to the routing theory, it has no sense to have 2
> interfaces on the same net.
> At least, on Cisco routers is not allowed.

It would make much more sense to have two routers connected to the same subnet... VRRP/HSRP, separate IPv4 and IPv6 routers. If the two interfaces 
are bridged together, there is no obvious benefit to having a secondary interface, which is sort of what the result below would accomplish. Decent 
routers would be doing everything in hardware...

Perhaps it would be wise to figure out what they really want, maybe by asking what they think that want, and then telling them how it should be 
done... If they want to have more bandwidth with two router interfaces, there are better solutions to this problem. If it were seriously a /16 subnet 
on the customer side, that pretty much means they aren't doing any routing that I would want to have a part of on their side. I hope those are 
examples with really wacky subnets, because that is pretty unrealistic.

So, no, no good reason. They probably are trying to do something and need some guidance, perhaps they should post what they want to do here. I am 
sure they will get some "interesting" responses.


> -----Mensaje original-----
> De: Sugar, Sylvia [mailto:truesylvia at]
> Enviado el: Martes, 11 de Noviembre de 2003 05:36 a.m.
> Para: nanog at
> Asunto: Router with 2 (or more) interfaces in same network
> I am curious to know if its possible to have a router with its two
> interfaces, say configured as,
> and Theoretically, i see nothing which can stop a
> router from doing this.
> But practically, is it of any use? And if used, then, when and why will
> somebody want to use such
> a kind of configuration?

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