Subject: Re: dhcpd(8) _cannot_ be completely disabled on an interface
To: Bill Squier <>
From: David Maxwell <>
List: tech-net
Date: 01/14/2002 17:13:37
On Wed, Jan 09, 2002 at 11:49:45PM -0500, Bill Squier wrote:
> On Wed, Jan 09, 2002 at 10:34:24PM -0500, Andrew Brown wrote:
> > >} netbsd, as i understand it, doesn't do proxy arp without the help of a
> > >} small daemon, somewhat like rarpd.
> > >
> > >     Yes it does.  What do you think "arp -s ... ..." would do?  This
> > >is the same mechanism that the "proxyarp" option of pppd would use.
> > 
> > it sets an ethernet <-> ip address mapping in the kernel's routing
> > table.
> ...and optionally publishes it.  man 8 arp.
> [...] If the word pub is given,
> > and i can't add a mapping for an ip address that's not on my
> > local network using arp(8).     
> s/my local network/one of &/
> Of course not.  Of what possible use would that be?

See RFC1027.

proxy-arp for entire supernets is used in several applications.

Anytime two hosts on the same physical wire disagree on the subnet size,
having a host that does proxy-arp for the entire 'true' subnet is

This sometimes happens during migration from one subnet size to another,
when some hosts have been updated, but others haven't.

It sometimes is used when certain hosts only support a classful routing
protocol, like RIP v1, and they have to believe they're on a simple
Class C, even though they're not.

It's used a lot in half-routed, half-bridged setups, like PPP terminal
servers, or certain cable modems, where the server end wants to treat the
clients as a single big subnet, but the clients can't ARP for other

It's probably a solution in some cases of NBMA networks, such as
partially meshed frame relay, or ATM links, though it's not the approach
I would take.

> You should really read about arp and dhcp before continuing a discussion
> about them.  :-)

RFC1027 is from 1987 - someone else is behind on their reading
assignments ;-)

> -- 
> Bill Squier (                
>         I know I don't deserve another chance, but this _is_ America,
>         and as an American, aren't I entitled to one?  --Sideshow Bob.

David Maxwell,| --> Mastery of UNIX, like
mastery of language, offers real freedom. The price of freedom is always dear,
but there's no substitute. Personally, I'd rather pay for my freedom than live
in a bitmapped, pop-up-happy dungeon like NT. - Thomas Scoville