<P> DHCP is used for Internet Protocol version 4 (IPv4) and IPv6 . While both versions serve the same purpose, the details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols . For the IPv6 operation, devices may alternatively use stateless address autoconfiguration . IPv6 hosts may also use link - local addressing to achieve operations restricted to the local network link . </P> <P> The DHCP employs a connectionless service model, using the User Datagram Protocol (UDP). It is implemented with two UDP port numbers for its operations which are the same as for the BOOTP protocol . UDP port number 67 is the destination port of a server, and UDP port number 68 is used by the client . </P> <P> DHCP operations fall into four phases: server discovery, IP lease offer, IP lease request, and IP lease acknowledgement . These stages are often abbreviated as DORA for discovery, offer, request, and acknowledgement . </P> <P> The DHCP operation begins with clients broadcasting a request . If the client and server are on different subnets, a DHCP Helper or DHCP Relay Agent may be used . Clients requesting renewal of an existing lease may communicate directly via UDP unicast, since the client already has an established IP address at that point . Additionally, there is a BROADCAST (B) flag the client can use to indicate in which way (broadcast or unicast) it can receive the DHCPOFFER: 0x8000 for broadcast, 0x0000 for unicast . Usually, the DHCPOFFER is sent through unicast . For those hosts which cannot accept unicast packets before IP addresses are configured, this flag can be used to work around this issue . </P>

Final step of the dhcp discovery process is known as