Subject: Re: Proxy ARP
To: Ignatios Souvatzis <firstname.lastname@example.org>
From: Erik E. Fair <email@example.com>
Date: 05/24/1998 03:04:00
Actually, proxy-arp applies when an ARP request is received that asks for a
host that the router knows is not on the same wire by dint of network mask,
and for which it has a route (typically other than "default", though an
argument can be made for proxy-arp in that case too). The router replies with
its own Ethernet station address and everything works because the packets will
be routed correctly to their destination.
Proxy-arp was the recommended way to deal with hosts on a subnetted LAN which
did not themselves implement subnetting (since, not knowing the subnet mask,
they'll simply ARP for all hosts in the LAN), though, as a side effect, it
also took care of hosts that are simply misconfigured (i.e. default netmask
for the "natural" address class, as opposed to the typically longer subnet mask).
So, what I was asking about is a default behavior in a modern IP router, rather
than something explicitly "turned on" or configured through the "arp" command,
on a per-address basis.
Does that clarify my question a bit better?
Erik E. Fair firstname.lastname@example.org