Re: Proxy ARP

[christos%astron.com@localhost (Christos Zoulas)]

In article <CAKrYomjukGiXD+COWino3rTDd_u+0o+q04aWxv_qn0GCM-GOgQ%mail.gmail.com@localhost>,
Ryota Ozaki  <ozaki-r%netbsd.org@localhost> wrote:
>Hi,
>
>I have questions about the Proxy ARP feature.
>
>arp(8) has two options: "pub" and "pub proxy".
>What's the different between them and what
>are expected behaviors of them?
>

Proxy arp (rfc1027) was used decades ago to make hosts whose
networking stacks did not understand subnetworking and routing
work (in my environment those were SVR2 machine AT&T 3b{2,5,10,20}s).
Typically we used to run a daemon on the gateway host that
watched for bogus arp requests (requests for addresses not in the
local broadcast domain/subnet that could not be satisfied) and
reply to them by saying that the gateway host(*) had the address
required and add this address to the arp table as a proxy entry.

I don't remember what was special about proxy arp entries, but my
guess is probably nothing; it was just a special marker to recognize
that these were added manually just for proxying.

The two plausible reasons would be:
	- not to time them out (but that would not make sense
	  because proxyarpd did not have any timeout code, so these
	  would become permanent
	- not to consult them for local routing decisions, but this
	  is not done anyway

You can still get a copy of a proxyarpd implementation from:

	ftp://mirror.ucsd.edu/pub/proxyarpd-1.7.shar

christos

(*) It ended being more complicated than that for hosts with multiple
gateways.  There was a "proxytab" file which said which
interfaces/ip-addresses where responsible for what subnets.