Proxy ARP (was Re: Dumb vs. smart host routing)


John Romkey (spdcc!kaos!romkey@bbn.com)
15 May 88 06:44:22 GMT


Bill,

I hate to do this, but I don't like proxy ARP at all.

There are two reasons for why:

First, there are too many network media that don't use ARP for my
taste. ARPANET, X.25, ProNET-10. Maybe FDDI won't? I look at what you
said about these media this way: you're going to have to support
default gateways on them. You want the vendor to support it. The
vendor's IP layer should probably be pretty media-independent, so if
you've got default routers working in the software when you hook up a
system to the ARPANET, you've basically got what you need for ethernet
too. So it's not really an extra work to support it for networks other
than the non-ARP media.

Second, I had a really bad experience with an ethernet at MIT that had
a proxy ARP router on it a few years ago. Dave Bridgham was setting up
a second IP subnet on an ethernet at LCS. But a strange thing was
happening - his packets were disappearing. The proxy ARP router was
sending out ARP replies few milliseconds after the host Dave was
trying to talk to and it ended up gobbling up all the packets. It took
us a long time to track down the problem.

I think there are situations where you might want to set up a second,
test IP subnet or network on an network cable which already has a
different IP subnet or network on it, and that proxy ARP routers which
might believe they're doing exactly the right thing would make it
impossible to do this.

So proxy ARP is unacceptable to me.

--
			- john romkey
UUCP: UUCP: romkey@kaos.uucp			ARPA: romkey@xx.lcs.mit.edu
 ...harvard!spdcc!kaos!romkey		Telephone: (617) 776-3121



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