DHCP question: dhclient won't request same IP.

[Dave Johnson]

Scott Garman writes:
> To test things further, I placed both machines behind a Linux DHCP
> server so I could look for any unusual error messages. Sure enough, I
> found the following in my logs after the Debian system exhibited the
> IP-changing behavior. The Debian system started out with IP
> 192.168.1.215, and ended up with 192.168.1.210:
> 
> Jan 31 12:32:03 dhcpd: DHCPDISCOVER from 00:d0:c9:9e:ae:59 via eth1
> Jan 31 12:32:03 dhcpd: ICMP Echo reply while lease 192.168.1.215 valid.
> Jan 31 12:32:03 dhcpd: Abandoning IP address 192.168.1.215: pinged
> before offer
> Jan 31 12:32:03 dhcpd: Wrote 0 deleted host decls to leases file.
> Jan 31 12:32:03 dhcpd: Wrote 0 new dynamic host decls to leases file.
> Jan 31 12:32:03 dhcpd: Wrote 9 leases to leases file.
> Jan 31 12:32:05 dhcpd: DHCPDISCOVER from 00:d0:c9:9e:ae:59 via eth1
> Jan 31 12:32:06 dhcpd: DHCPOFFER on 192.168.1.210 to 00:d0:c9:9e:ae:59
> via eth1
> Jan 31 12:32:08 dhcpd: DHCPREQUEST for 192.168.1.210 (192.168.1.1) from
> 00:d0:c9:9e:ae:59 via eth1
> Jan 31 12:32:08 dhcpd: DHCPACK on 192.168.1.210 to 00:d0:c9:9e:ae:59 via
> eth1


It appears the client is sending a DHCPDISCOVER while still using the
old address (the server can ping it).

For a renewal of an existing lease the client should first send a
DHCPREQUEST instead of DHCPDISCOVER.  Only if the DHCPREQUEST is
ignored/lost should it send a DHCPDISCOVER in an attempt to find a new
lease.

The server is doing the right thing in this case.  If the server
recieved a DHCPREQUEST first it would extend the existing lease.

The logs from the client computer may reveal the requests and if it is
trying a REQUEST first with no response.


-- 
Dave