Re: Proxy ARP

[Robert Elz <kre%munnari.OZ.AU@localhost>]

When a host is answering ARP queries for an IP address that is not its
own, there are two ways (and reasons) for how it does that.

It can send its own MAC address (kind of claiming ownership of the
IP address, though all it will usually do with the packet is relay it 
elsewhere.)

Or it can send someone else's MAC address - so that the host that sent
the query gets told the MAC address of the owner of the IP address (one
hopes.)  This was used in the ancient times Christos mentioned when some
hosts existed that did not understand ARP (IP over ethernet existed before
ARP was invented.)

One of those was known as proxy ARP, the other wasn't - but I'm not sure
the nomenclature has remained consistent over time.  Any rational need for
the second form vasnished long long ago, I can't imagine any host still
running which understands both IP and ethernet, but not ARP.

I suspect from a (very very) brief look at the code, the "proxy" option
to arp(8) is meaning the 2nd of the two.

kre