This a Dynamic DNS enabled version of the DHCP client.
 .
 Dynamic Host Configuration Protocol (DHCP) is a protocol like BOOTP
 (actually dhcpd includes much of the functionality of bootpd). It
 gives client machines "leases" for IP addresses and can
 automatically set their network configuration. If your machine
 depends on DHCP (especially likely if it's a workstation on a large
 network, or a laptop, or attached to a cable modem), keep this or
 another DHCP client installed.
 .
 Extra documentation can be found in the package isc-dhcp-common.