[Dnsmasq-discuss] When Client is set to DHCP

Simon Kelley simon@thekelleys.org.uk
Tue, 30 Nov 2004 07:58:19 +0000

Ross Williams wrote:

> 1. Configure on the client the DHCP 'host-name' option to whatever 
> hostname you want that client to be known as in dnsmasq. Some client 
> software seems to interchangeably refer to the host-name option as the 
> client ID option, although the two are different. The dnsmasq man page 
> refers to both the host-name option and the client-id option, and I 
> believe that they are handled differently. Simon or someone else, 
> however, would have to answer that question.

Think of client-ids as a stable indentifier for the system: what most 
people use the MAC address for. The idea is that the client-id can be 
derived from something like a motherboard serial number or OS install, 
and then a faulty network interface could be swapped out without 
disturbing the configuration of the DHCP server. In practice most DHCP 
clients either don't send a client-id (in which case the MAC address is 
used instead) or they send the MAC address as the client-id, so the 
practical effect is zero.

In any case host-name is not equal to client-id. A machine could change 
its host name and still be given the same IP by DHCP. If it changed 
client-id it would be seen as a new machine and given a new IP address.