one ethernet get more than one ip address

Simon Hobson dhcp1 at
Thu May 10 16:07:19 UTC 2012

Julie Xu wrote:

>I have found for some reason, one ethernet address may get more than 
>one ip address in my dynomic range, something like 2-6 ip addresses.

Can you show us a couple of lease file entries showing this ?

The usual reason is that the client, or multiple clients on one 
device, have used different Client IDs.

As an example of different clients, consider a machine that boots 
different OSs. It may boot with PXE (no client ID) and then into 
Windows (uses MAC address as Client ID). Or it may boot sometimes 
into Linux (no Client ID) and sometimes into Windows.

As an example of "same client", some versions of Windows 
automatically obtain themselves several addresses (used to be 10 in 
NT which was the last time I had to deal with it) "just in case" a 
remote access client should dial in. In the majority of cases there 
is no RAS being used, but the service used to be installed and 
started automatically. The machine would get an address for itself 
(using MAC address for Client ID), and several for clients (using 
multiple Client IDs starting with "RAS ").

The standards require that the Client ID be used as the primary key 
if one is supplied, and the MAC (Hardware) address is only used if no 
Client ID is present. This means that requests using different Client 
IDs are considered as different clients and so will obtain different 

Simon Hobson

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