two interfaces one subnet - SOLVED

Chris Meidinger cmeidinger at
Mon May 11 17:00:52 CDT 2009

On 11.05.2009, at 23:39, Mike O'Connor wrote:

> :Hi,
> :
> :This is a pretty moronic question, but I've been searching RFC's on-
> :and-off for a couple of weeks and can't find an answer. So I'm hoping
> :someone here will know it offhand.
> :
> :I've been looking through RFC's trying to find a clear statement that
> :having two interfaces in the same subnet does not work, but can't  
> find
> :it that statement anywhere.
> :
> :The OS in this case is Linux. I know it can be done with clever
> :routing and prioritization and such, but this has to do with vanilla
> :config, just setting up two interfaces in one network.
> :
> :I would be grateful for a pointer to such an RFC statement, assuming
> :it exists.
> RFC1122, Section explicitly says this IS a legal config
> from an IP perspective:
>      3.3.4  Local Multihoming
>  Introduction
>            A multihomed host has multiple IP addresses, which we may
>            think of as "logical interfaces".  These logical interfaces
>            may be associated with one or more physical interfaces, and
>            these physical interfaces may be connected to the same or
>            different networks.
> There are other considerations here -- OS, link-layer, etc.
> Obviously, you want to do such things with care.  But simply
> from a "standards" perspective, it's ok.  There are a lot of
> hosts that historically didn't have enough RFC1122 compliance
> to make such configurations problematic (e.g. section
> and multiple default route support vs. old BSD IP stacks) but
> that doesn't invalidate the standards.

Thank you!

This is what I (wasn't) looking for, but was destined to find. I'll  
look for other arguments against the practice.

And again, because I didn't say it before: Thanks for the pointer!!  
This is just what I was looking for to stop looking.



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