Subject: DHCP server startup announcement

From: Stuart Cheshire <[email-masked]>
Date: Fri, 22 Sep 2000 13:40:08 -0700

When a DHCP client fails to find a DHCP server, it typically keeps 
broadcasting DHCP DISCOVERs at a low rate (e.g. one every five minutes).

Now that so many home users are beginning to use home networks, both 
wired and wireless, we have a lot more casual users of the DHCP protocol. 
A not-too-infrequent scenario is that the user turns on a client machine, 
finds that it isn't working properly, and discovers that this is because 
the gateway/DHCP Server box was not turned on. They then turn on the 
gateway box, and expect the client machine to work, but it could be up to 
five minutes before the next DISCOVER is sent out.

Some Operating Systems today adopt the solution of having special tools, 
command-line programs or Control Panels where the user can take some 
special action to reset the DHCP client, but I think it would be much 
better if it just worked automatically, so that the user didn't have to 
know or care about special tools like this. Computers should "just work". 
In this spirit, I think it would be a good idea if a DHCP server 
broadcast a few "announcement" packets when it starts up, to let waiting 
clients know that a DHCP server is now available.

One thought that occurs to me is that we could borrow from 
draft-ietf-dhc-pv4-reconfigure-01.txt -- the server could broadcast a 
FORCERENEW (perhaps with all zeroes in the chaddr field) effectively 
saying, "To any client that currently has no server-assigned address, and 
would like one, a server is now available for you to send a DISCOVER."

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer
 * Chairman, IETF ZEROCONF
 * www.stuartcheshire.org

---

From: Erik Guttman <[email-masked]>
Date: Mon, 25 Sep 2000 09:00:29 +0200 (MET DST)

> broadcasting DHCP DISCOVERs at a low rate (e.g. one every five minutes).
...
> would like one, a server is now available for you to send a DISCOVER."

I fully support this direction.  This will make it much easier for
auto configured clients to discover DHCP servers.  One of the problems
with the 'polling model' is that devices will discover the DHCP server
at different times.  During this 'transition' phase, some devices could
potentially be unable to communicate.  This could be avoided by having
devices discover the DHCP server through an announcement and transition
en masse.  Considering that - there should be some randomizing interval
so that hosts that receive the FORCERENEW don't all try to hit the DHCP
server at once :-)

Erik