Article 16596 of comp.dcom.lans.ethernet:
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From: sthaug@nethelp.no (Steinar Haug)
Newsgroups: comp.protocols.tcp-ip,comp.dcom.lans.ethernet
Subject: Re: Multiple subnets on the same physical media
Date: 25 Oct 1996 20:47:00 GMT
Organization: Nethelp Consulting, Trondheim, Norway
Lines: 21
Distribution: world
Message-ID: <54r904$8vv@verdi.nethelp.no>
References: <54o33o$8ps@darling.cs.umd.edu> <1996Oct25.145928@netman.eng.auburn.edu>
NNTP-Posting-Host: aun.uninett.no
In-reply-to: doug@eng.auburn.edu's message of Fri, 25 Oct 1996 14:59:28 CDT
Xref: mri.com comp.protocols.tcp-ip:30606 comp.dcom.lans.ethernet:16596

[Doug Hughes]

| > Assume a Host x on Subnet X wants to talk to a host y on the subnet Y,
| > where both subnets X and Y share the same physical media (say ethernet).
.
| > 2) Is there (an RFC compliant) mechanism by which x and y could talk
| > 	 using link-layer mechanisms only.
|   
| If the hosts support multiple addresses (like SunOS5, NetBSD, FreeBSD, Linux)
| you can just bring up another virtual interface on the other subnet number
| and they can talk directly that way.  If a host does not support virtual
| interfaces but has two network cards, you 'may' be able to do something
| similar (depending on if the two interfaces share the same MAC address as
| on some machines). Otherwise, you'll probably want to use a router of
| some sort.

Or you can use the good old 'arp hack' - install a default route pointing
to the host itself (metric 0), and let the real router take care of the
connections to the rest of the world with proxy ARP.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no