Cisco IOS DHCP Manual bindings for dummies

So I was screaming and ranting (not really, but dramatic effect always works… right?… what?.. it doesn’t? hmm…)

I use a Cisco 385 router (or is it 580, 850, 857, I can’t remember) to keep my network together and connect it to the outside world. It does a great job at most trivial things (except for IPv6 which is non-existant, and thus it will soon be replaced by a 1841 probably) and I have fun forwarding ports and whatnot.

The thing that however puzzled me was the fact that manual IP/DHCP bindings for computers in my local network were sometimes accepted, and sometimes not. I had “read” (as in read fast and inaccurate) the manual and came up with simple entries like:

ip dhcp pool afancyname
host 192.168.0.10 255.255.255.0
hardware-address 0012.3456.789a
client-name afancyname

And after fiddling around with settings in Windows for weeks, I finally started actually reading the manual and stumbled upon the difference between “hardware-address” and “client-identifier”.

The big difference (next to a simple 01 prefix to the mac-address) is that hardware-address is for BOOTP, and client-identifier is for DHCP. Client-Name is also BOOTP only, and should not be used.

So I looked up the Client-identifier via “sh ip dhcp bindings” and wrote the following config bit instead:

ip dhcp pool afancyname
host 192.168.0.10 255.255.255.0
client-identifier 0100.1234.5678.9a

Et voila, release and renew your IP address client-side, and you have your preferred IP address.

However, ofcourse this is only because Windows supplies the client-identifier argument with its DHCPRequest packet, and Linux for some reason does not. So for Linux hardware we need to fallback on hardware-address (unless you manually edited your dhclient.conf file it seems):

ip dhcp pool myfancylinuxpc
host 192.168.0.11 255.255.255.0
hardware-address 0012.3456.789b