Path: utzoo!attcan!uunet!husc6!uwvax!oddjob!ncar!ames!pasteur!ucbvax!UM.CC.UMICH.EDU!Doug_Nelson
From: Doug_Nelson@UM.CC.UMICH.EDU
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Dumb vs. smart host routing
Message-ID: <3056313@um.cc.umich.edu>
Date: 17 May 88 16:35:46 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 19

> As far as I know, "Proxy ARP" only works with subnets, for nodes that
> don't know about subnets.   In order to send out the ARP request, the
> host has to already belive that he can get to the remote host in one
> hop.  If my machine is on net 128.62, and I want to get to a machine on
> net 128.63, I don't send out an ARP request for the machine on net 128.63.
> I have to have a route to 128.63 which points to a machine on net 128.62,
> and then I'll be ARPing for the machine on 128.62 which is the next hop to
> 128.63.
 
Proxy ARP also works in networks where the gateway(s) aren't using
any routing protocol at all.  We teach many of our systems here
that the default route is to themself, with a metric of zero.
This forces an ARP for most hosts outside the (sub)network, whether
within or outside the full network.
 
It helps that we only have one gateway to the outside world.
 
Doug Nelson, Michigan State University, Computer Lab
den@serv1.cl.msu.edu