Migration

Since DHCP is based on BOOTP and the BOOTP packet structure, migrating to DHCP is easy for most sites. Many DHCP servers support both old BOOTP and new DHCP clients.

Since the Solaris 2 DHCP server handles BOOTP queries as well as DHCP queries, a BOOTP client can boot from a DHCP server. If a DHCP client is written to use the answers from a BOOTP server, a DHCP client can boot from a BOOTP server. The TCP/IP stack included with Windows 95 does not have this capability.

Subnets

DHCP client messages are sent to remote servers by BOOTP relay agents, which are often a feature of an IP router. Through the BOOTP relay agent, the DHCP server can tell which subnet a request came from. The BOOTP relay agent records which subnet the message came from in the DHCP message header. Then the DHCP server can use it to determine which network the client is on.

You cannot run a BOOTP server and a DHCP server on the same machine, because they both use the same port number. You can use the Solaris 2 DHCP server to serve BOOTP clients by turning on BOOTP compatibility mode.

With the DHCP protocol, a client that already has a leased or permanent IP address can get another lease on a temporary basis on another subnet. This is helpful for machines that sometimes must be moved from one location to another. This option is available if the server implementation supports such a feature.

Routers

DHCP requires non-volatile storage. This makes the task of DHCP service compatible with servers, but incompatible with dedicated routers. There are a number of server types that can be configured to both relay and serve DHCP, especially all-in-one Internet Gateways designed to be web servers, firewalls, and so forth. But there are no dedicated routers.

The DHCP RFC specifies that DHCP is not intended for use in configuring routers. The reasons are that in maintaining and troubleshooting a router, it is important to know its exact configuration, rather than leaving that to be established automatically, and that you do not want your router's operation to depend on the working of yet another server.

You may be able to configure some types of more general purpose computers or servers to get their IP addresses from DHCP and to act as routers. In addition, there are remote access servers, which are usually not true routers, which use DHCP to get IP addresses to give to their clients.