Leases

When the DHCP server gives out an IP address it gives it out as a lease for a certain amount of time. This is given in seconds in the default-lease-time variable in the configuration file. The server stores a list of all the leases and their expiration dates in a file called /var/lib/dhcp/dhcpd.leases. This is what an entry in the file looks like:

lease 1.2.3.221 {
        starts 2 2002/03/26 02:23:59;
        ends 3 2002/03/27 02:23:59;
        hardware ethernet 33:44:55:66:77:88;
        uid 01:23:45:67:89:ab:cd;
        client-hostname "robert";
}

Sometime you do not get all of the information listed above, but you always get the starting time, the ending time, and the ethernet address. With the information in the dhcpd.leases file you can setup static DHCP where the same IP address is given to the same ethernet address every time.