The Role of DHCP Agents
The DHCP relay agent makes it possible to put DHCP (dynamic host configuration protocol) servers and clients at various networks. This represents several advantages for the network administrator.
Multisegment Networks and DHCP
Every DHCP message is an IP broadcast. Every computer at the segment can hear and respond to it. One scope on the server will be enough. The problem arises when there is more than a single subnet.
The protocol does not usually cross the interfaces of routers. A large company will have a difficult time putting a protocol server at every segment. It is time consuming and costly.
How DHCP Relay Agents Help
Instead of adding more servers, the agents can be used instead. This allows you to install fewer servers that are stationed centrally. The broadcast message problems are resolved by setting up the routers to go by the messages of DHCP/BOOTP. This is known as BOOTP Relay.
The BOOTP Relay and Forwarding concepts are not the same. In the latter the message is sent forward to another interface sans unique processing. With relay, there is a more intricate procedure. It may also mean altering the packet.
The Role of the Agent
The agent is not a Forwarder. A router that can do BOOTP Relay can forward more than BOOTP messages. The agent will scrutinize the packet. It will then make the appropriate changes. This will then be sent to the protocol server. The server where the packet is sent is set up with the addition of a Helper Address.
There are routers which have no support for BOOTP Relay. If this is the situation, you can establish a computer on parts with DHCP clients that will replace the BOOTP agent. For instance, you can set up Windows 2000 RRAS Server to send protocol messages by installing the proper agent.
The agent will interact with the server and function as a proxy for the messages that will be relayed to other segments. The protocol agent can be set up with DHCP server addresses to where the message will be sent.
It is important that you know the difference between a router and an agent. The router functions as a forwarder of BOOTP. The forwarders spread the message being broadcast along router interfaces.
The agent will intercept this. It will then change the protocol message. It is then relayed by way of a directed datagram to a protocol server.