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