I'll be quite honest and say I haven't done a detailed investigation
of the IOS implementation restrictions here. My intuition would be
that IOS has one ARP cache per subnet per physical router, and having
multiple router ports in the same broadcast subnet confuses the ARP
mechanism. On a first scan of RFC 1812, I don't see any inherent
architectural limitation on more than one interface in a subnet on a
physical router.
I suspect the reason that multiple serial interfaces can work is that
they don't routinely ARP, since they don't have to resolve MAC
addresses they don't have.
>However, just in the last few days, we read on this list that serial
>interfaces can have 2 or more in the same subnet. I think one poster said
>there was a maximum of 6?
Which would be consistent with the maximum interfaces in load
sharing. I suspect there are some IOS internal games here, where an
(internal only) virtual interface describes the next hop for a
destination to which there is load sharing, and some type of
recursion takes place (perhaps interacting with a cache) to decide
which physical interface to use.
These are guesses, however.
>
>But ethernet interfaces cannot share a subnet.
>
>Kevin Wigle
>
>----- Original Message -----
>From: "John Neiberger" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Cc: <[EMAIL PROTECTED]>
>Sent: Friday, 30 March, 2001 10:41
>Subject: Re: Stupid question
>
>
>> This isn't a stupid question, it's a very important point to make. If
>> you are routing, each interface on the router must be in its own subnet.
>> Otherwise routing would not work. If you're bridging, then the bridged
>> interfaces are in the same subnet but you don't specifically assign an
>> IP address to those interfaces.
>>
>> I'm guessing that you're really asking the former question: in a
>> routing situation can two different interfaces be in the same subnet,
> > and the answer is no.
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