Setting Up DHCP Relay Agents

In an ideal configuration, you'll have multiple DHCP servers on each subnet. However, because this isn't always possible, you can configure your routers to forward DHCP broadcasts or configure a computer on the network to act as a relay agent. Any computer running Windows Server 2003 can act as a relay agent. Doing so requires that Routing and Remote Access be configured and enabled on the computer first, and then you can configure the computer as a relay agent using the Routing And Remote Access console.

Configuring and Enabling Routing and Remote Access

To start the Routing And Remote Access console, click Start, Programs or All Programs, Administrative Tools, Routing And Remote Access. If the computer you want to use as the relay agent isn't listed as an available server, right-click the Routing And Remote Access node in the left pane, and select Add Server. In the Add Server dialog box, select The Following Computer, type the name or IP address of the computer, and then click OK.

If the computer isn't already configured for Routing and Remote Access, right-click the computer node in the left pane, and then select Configure And Enable Routing And Remote Access. This starts the Routing And Remote Access Setup Wizard. Click Next. Choose Custom Configuration, as shown in Figure 25-25, and then click Next again. On the Custom Configuration page, select LAN Routing. Click Next, and then click Finish. Click Yes when prompted to start the Routing and Remote Access Service.

Configure and enable Routing and Remote Access.

Figure 25-25. Configure and enable Routing and Remote Access.

Adding and Configuring the DHCP Relay Agent

In the Routing And Remote Access console, expand the node for the computer you just configured, and then expand IP Routing. Right-click the General node, and then choose New Routing Protocol. In the New Routing Protocol dialog box, select DHCP Relay Agent, and then click OK. This adds an entry under IP Routing labeled DHCP Relay Agent.

In the Routing And Remote Access console, right-click the DHCP Relay Agent entry, and choose New Interface. The New Interface For DHCP Relay Agent dialog box is displayed, as shown in Figure 25-26, showing the currently configured network interfaces on the computer. Select the network interface that is connected to the same network as the DHCP clients whose DHCP broadcasts need forwarding, and then click OK.

Select the network interface on the same network as the DHCP clients.

Figure 25-26. Select the network interface on the same network as the DHCP clients.

The DHCP Relay Properties dialog box is displayed automatically, as shown in Figure 25-27. You have several configurable options:

  • Relay DHCP Packets When selected ensures DHCP packets are relayed.

  • Hop-Count Threshold Determines the maximum number of relay agents a DHCP request can pass through. The default is 4. The maximum is 16.

  • Boot Threshold (Seconds) Determines the number of seconds the relay agent waits before forwarding DHCP packets. The delay is designed so that local DHCP servers will be the first to respond if they are available. The default delay is 4 seconds.

Set the relay options.

Figure 25-27. Set the relay options.

After you set the relay options, click OK. In the Routing And Remote Access console, rightclick the DHCP Relay Agent entry, and choose Properties. This displays the DHCP Relay Agent Properties dialog box. Type the IP address of the DHCP server to which DHCP packets should be forwarded, and then click Add. Click OK. The computer is then configured as a DHCP relay agent.

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