ZenLinux Blog

I’m working with Debian Sarge (stable) on an embedded Linux device at work, and recently wasted a lot of time tracking down problems with DHCP. Specifically, the client was changing IP addresses intermittently during a DHCP lease renewal – not cool. So I put the device behind another Linux system running its own DHCP server, and found the following clue in the logs:


dhcpd: DHCPDISCOVER from 00:d0:c9:9e:ae:59 via eth1
dhcpd: ICMP Echo reply while lease 192.168.1.215 valid.
dhcpd: Abandoning IP address 192.168.1.215: pinged before offer
dhcpd: Wrote 0 deleted host decls to leases file.
dhcpd: Wrote 0 new dynamic host decls to leases file.
dhcpd: Wrote 9 leases to leases file.
dhcpd: DHCPDISCOVER from 00:d0:c9:9e:ae:59 via eth1
dhcpd: DHCPOFFER on 192.168.1.210 to 00:d0:c9:9e:ae:59 via eth1
dhcpd: DHCPREQUEST for 192.168.1.210 (192.168.1.1) from 00:d0:c9:9e:ae:59 via eth1
dhcpd: DHCPACK on 192.168.1.210 to 00:d0:c9:9e:ae:59 via eth1


Interesting… Some research (and help from the folks on the GNHLUG discussion list) uncovered that the client was sending a DHCPDISCOVER while still using the old address. When a DHCP lease is being renewed, the client is supposed to send a DHCPREQUEST, not DHCPDISCOVER.

So why on earth was it doing this in the first place? My only explanation is that the dhcp-client package that Debian Sarge comes with (v2) isn’t following the specification correctly. I have no idea how old that package is, but I do know that nearly all of the modern Linux distros I’ve used for years come with dhcp3-client. Fortunately, the Debian stable repositories include dhcp3-client – it’s just not the default client!

The lesson from all of this?: don’t assume that just because a package is in Debian’s default stable install you can take its correct operation for granted.