How to request a specific IP address from DHCP server?

using the linux program dhclient.

If you don't have linux installed, you can use a bootable Linux live CD.

[edit] If you do this trick to create an address reservation for an actual Windows machine, first switch the NIC in Windows to a static IP, because after a reboot in DHCP mode Windows may send a DHCP request with its last used IP, which would annihilate your efforts with dhclient below...

The trick is to send a DHCP request with your desired IP address from the same NIC (or better: same MAC address).

Edit the /etc/dhcp/dhclient.conf and add the following line (you might have to first copy the file to a writeable location if booting from a CD):

send dhcp-requested-address 192.168.1.240;

Then stop and start dhclient as user root, where your NIC is eth0 (check by issuing ip addr show beforehand)

dhclient -r -v
dhclient -4 -d -v -cf /etc/dhcp/dhclient.conf eth0

If successfull, your DHCP server will fulfill your prepared request. Sometimes you will have to delete the device entry in the DHCP table before issuing dhclient -4 -d ....

Then make that device IP address in the DHCP table of the router a fix address reservation. This will associate the IP to the MAC of the device and return the same IP everytime a DHCP request with that MAC address is encountered in the future.