Re: Proxy ARP

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

    Date:        Mon, 7 Mar 2016 19:31:34 +0900
    From:        Ryota Ozaki <ozaki-r%netbsd.org@localhost>
    Message-ID:  <CAKrYomjaaRzpSKaDCq6hy049ZV=rcMCh-jsYjVcp2WWRxKTEUg%mail.gmail.com@localhost>

  | > On Thu, Feb 25, 2016 at 12:57:59PM +0000, Christos Zoulas wrote:
  | >> In article <CAKrYomjukGiXD+COWino3rTDd_u+0o+q04aWxv_qn0GCM-GOgQ%mail.gmail.com@localhost>,
  | >> Proxy arp (rfc1027) was used decades ago to make hosts whose
  | >> networking stacks did not understand subnetworking and routing

  | On Thu, Feb 25, 2016 at 11:24 PM, Joerg Sonnenberger
  | <joerg%britannica.bec.de@localhost> wrote:

  | > I have used it much more recently for VMs and the like. If you
  | > configure the host machine to provide proxy ARP and use point-to-point
  | > links for the individual machines,

Those two are both examples of the more modern (still relevant, at
least in the second case) use of some form of proxy arp.   Many
commercial routers (still) do this to compensate for misconfigured
hosts.   In both cases the host answering would be acting as a router,
and forwarding packets where they're intended.

The first of those (Christos' case) could in the very early days have
been an instance of the other use though - before the router (if it was not
a BSD host) understood any kind of proxy arp, some other host could send
the router's MAC address to the host that was arping for an address that
is not on the local subnet.  Since these days all routers can manage that
for themselves, that (publish someone else's MAC address) form is not
longer likely to be required for this use either.

kre