Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!zen!ucbvax!AI.AI.MIT.EDU!JBVB
From: JBVB@AI.AI.MIT.EDU ("James B. VanBokkelen")
Newsgroups: comp.protocols.tcp-ip
Subject: Re: More than one IP (sub)network on one ethernet cable
Message-ID: <301351.871217.JBVB@AI.AI.MIT.EDU>
Date: 18 Dec 87 04:43:33 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 20

If a gateway is present, it should be configured as such.  If there is no
gateway, I can either return an error to the user, or ARP the address
on the other network anyway.  If it is on another subnet which has suddenly
become irrelevant, re-configure and unset the subnet bits.

If I ARP it, maybe it is a spurious broadcast, maybe it works.  If it
works, various clever bits of code that treat things routed via a gateway
differently break down, but the connection probably survives.  To me, the
tradeoffs have seemed to favor returning the error.  If the user is in the
what I think to be the mainstream, he has a configuration problem, and
should know about it.

Our code was recently reported (by a customer) to be willing to ARP any
address configured as a gateway, although it won't ARP off-net addresses
if no gateway is configured.  I didn't design it, but it seems reasonable.

Comments?

James B. VanBokkelen
FTP Software