Subject: ISC dhcp server implementation

From: Rhandeev Singh <[email-masked]>
Date: Wed, 21 Jul 1999 06:50:48 -0400 (EDT)

Hi Ted,

In a Virtual LAN environment, it is desirable to configure some DHCP
servers to ignore requests from clients whose chaddr is not recognized.

As we couldn't find a way to do this with version 2.0b1 of the ISC dhcp
server implementation, we decided to ask if we could implement this and
perhaps forward the patch to you. 

We believe that the introduction of this behaviour does not break
compliance with section 4.2 of RFC 2131, but correct us if we're wrong:

---------extract-from-rfc-2131---------------------
 4.2 DHCP server administrative controls

   DHCP servers are not required to respond to every DHCPDISCOVER and
   DHCPREQUEST message they receive.  For example, a network
   administrator, to retain stringent control over the clients attached
   to the network, may choose to configure DHCP servers to respond only
   to clients that have been previously registered through some external
   mechanism.  The DHCP specification describes only the interactions
   between clients and servers when the clients and servers choose to
   interact; it is beyond the scope of the DHCP specification to
   describe all of the administrative controls that system
   administrators might want to use.  Specific DHCP server
---------end-extract-from-rfc-2131-----------------
 
Thanks.

Rhan.

---
Rhandeev Singh
Linux User Group
National University of Singapore

---

From: Ted Lemon <[email-masked]>
Date: Wed, 21 Jul 1999 10:32:19 -0400 (EDT)

> servers to ignore requests from clients whose chaddr is not recognized.

You can in fact do this with Version 2.0 of the ISC DHCP server.   To
do it, you need to start your configuration file with:

not authoritative;
deny unknown-clients;

Then you need to write host declarations for every client, like this:

host client-1 { hardware ethernet 08:00:2b:4c:a9:ad; }

And then, of course, you need some kind of subnet and address range
declarations.

The "not authoritative" statement causes the DHCP server to respond
negatively only to clients that have host declarations - in other
words, it won't send DHCPNAK messages to unknown clients that happen
to have configurations the server thinks are incorrect.   The "deny
unknown-clients" statement tells the server not to supply leases to
clients that aren't registered.   The host statement registers a
client.

BTW, there is a mailing list for the ISC DHCP server - visit
http://www.isc.org for details.

			       _MelloN_