[114450] in North American Network Operators' Group
Re: two interfaces one subnet - SOLVED
daemon@ATHENA.MIT.EDU (Chris Meidinger)
Mon May 11 18:13:06 2009
From: Chris Meidinger <cmeidinger@sendmail.com>
To: "Mike O'Connor" <mjo@dojo.mi.org>
In-Reply-To: <20090511213951.GC28211@dojo.mi.org>
Date: Tue, 12 May 2009 00:00:52 +0200
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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 3.3.4.1 explicitly says this IS a legal config
> from an IP perspective:
>
> 3.3.4 Local Multihoming
>
> 3.3.4.1 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 3.3.1.2
> 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.
Best,
Chris
