Strange Client Behavior

[Glenn Satchell]

>From: "David E. Bruce" <dbruce at uark.edu>
>Date: Thu, 3 Dec 2009 17:04:38 -0600
>
>I've got a client on my network that is requesting an IP, receiving it  
>from the DHCP server, and then turning around and asking for another  
>one within a few minutes.  The server is then providing a second IP.   
>The client then proceeds to request both IPs at the normal intervals  
>throughout the day.  Here's the log entry:
>
>Nov 25 07:51:13 192.168.1.1 dhcpd: DHCPDISCOVER from 00:1e:4f:a7:e1:c2  
>via eth0.222
>Nov 25 07:51:14 192.168.1.1 dhcpd: DHCPOFFER on 192.168.72.84 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 07:51:15 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.84  
>(192.168.1.1) from 00:1e:4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 07:51:15 192.168.1.1 dhcpd: DHCPACK on 192.168.72.84 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.222
>
>Nov 25 07:53:41 192.168.1.1 dhcpd: DHCPDISCOVER from 00:1e:4f:a7:e1:c2  
>via eth0.222
>Nov 25 07:53:42 192.168.1.1 dhcpd: DHCPOFFER on 192.168.72.188 to  
>00:1e:4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 07:53:42 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.188  
>(192.168.1.1) from 00:1e:4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 07:53:42 192.168.1.1 dhcpd: DHCPACK on 192.168.72.188 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.222
>
>Nov 25 09:51:47 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.84 from  
>00:1e:4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 09:51:47 192.168.1.1 dhcpd: DHCPACK on 192.168.72.84 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.222
>
>Nov 25 09:54:06 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.188 from  
>00:1e:4f:a7:e1:c2 (scasterxp) via eth0.224
>Nov 25 09:54:06 192.168.1.1 dhcpd: DHCPACK on 192.168.72.188 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.224
>
>Nov 25 11:51:51 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.84 from  
>00:1e:4f:a7:e1:c2 (scasterxp) via eth0.222
>Nov 25 11:51:51 192.168.1.1 dhcpd: DHCPACK on 192.168.72.84 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.222
>
>Nov 25 11:54:06 192.168.1.1 dhcpd: DHCPREQUEST for 192.168.72.188 from  
>00:1e:4f:a7:e1:c2 (scasterxp) via eth0.224
>Nov 25 11:54:06 192.168.1.1 dhcpd: DHCPACK on 192.168.72.188 to 00:1e: 
>4f:a7:e1:c2 (scasterxp) via eth0.224
>
>
>As far as I know, there's nothing to prevent the server from providing  
>the client with another IP, even though it already has a lease, is  
>that correct?  This looks like a client issue to me, but I'd thought  
>I'd ask if anyone has seen this before.
>

Hi David

It definitely is client behaviour. You can restrict each client to one
lease using

       one-lease-per-client true;

       If this flag is enabled, whenever a client sends a DHCPRE-
       QUEST  for  a  particular lease, the server will automati-
       cally free any  other  leases  the  client  holds.    This
       presumes  that when the client sends a DHCPREQUEST, it has
       forgotten any lease not mentioned  in  the  DHCPREQUEST  -
       i.e.,  the  client has only a single network interface and
       it does not remember leases it's holding  on  networks  to
       which  it  is  not  currently attached.   Neither of these
       assumptions are guaranteed or provable, so we urge caution
       in the use of this statement.

However you might wish to investigate the client first. It may be that
if it is a PC (wild guess based on hostname being *xp) that the user is
running a VM which is also requesting an IP.

What do the entries in dhcpd.leases look like?

regards,
-glenn