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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!killer!texbell!bellcore!jupiter!karn
From: karn@jupiter (Phil R. Karn)
Newsgroups: comp.protocols.tcp-ip,comp.dcom.lans
Subject: Re: Super Cheap IP router (< $1000)
Message-ID: <15134@bellcore.bellcore.com>
Date: 4 Apr 89 22:35:51 GMT
References: <583@accuvax.nwu.edu.NWU.EDU> <1989Apr4.000727.2759@utzoo.uucp> <25098@amdcad.AMD.COM>
Sender: news@bellcore.bellcore.com
Reply-To: karn@jupiter.bellcore.com (Phil R. Karn)
Organization: Bell Communications Research, Inc
Lines: 35

>Well, for one thing, Phil's code associates an IP address with the *host*,
>not with each interface. (See? KA9Q isn't *perfect*... yet.)

I consider that a feature, not a bug. :-)  Seriously, I have always
considered the Internet approach of giving addresses to interfaces
rather than to hosts to have been a bad move, and my approach of "one IP
address per customer" was a deliberate design decision based on how I
wanted the amateur packet radio TCP/IP network to evolve.

Nevertheless, you can still make my code emulate a conventional Ethernet
router with two distinct addresses by merely enabling proxy ARP. You
assign the router running KA9Q an address on each network. One of these
addresses becomes the host address for the system; the other is entered
into the ARP table with the "publish" subcommand such that it answers
ARP requests for that address with the Ethernet address of the
appropriate interface.

For example, consider a system with two Ethernet interfaces and two IP
addresses as follows:

Interface A:	Ethernet addr 02:60:8c:0:0:1	IP addr 1.2.3.4
Interface B:	Ethernet addr 02:60:8c:0:0:2	IP addr 44.0.0.1

The autoexec.net file would contain, among other things, the following
two lines:

ip address [1.2.3.4]
arp publish [44.0.0.1] ethernet 02:60:8c:0:0:2

This will make the system behave just as it should for purposes of
routing packets. The only precaution you have to make is to use the
router's "primary" IP address whenever you want to talk directly to it
as a host. Of course, it is then operating as a host, not a router...

Phil