Deploying a DHCP relay agent

Because they rely on broadcast transmissions, DHCPv4 clients can access DHCP servers only on the local network, under normal circumstances. However, it is possible to create a DHCP infrastructure in which one server provides addresses for multiple subnets. To do this, you must install a DHCP relay agent on every subnet that does not have a DHCP server on it.
Many routers are capable of functioning as DHCP relay agents, but in situations where they are not, you can configure a Windows Server 2012 R2 computer to function as a relay agent by using the following procedure.
1. In Server Manager, using the Add Roles And Features Wizard, install the Remote Access role, including the Routing role service.
2. Click Open The Getting Started Wizard. The Configure Remote Access Getting Started Wizard opens.
3. Click Deploy VPN Only. The Routing And Remote Access console appears.
4. Right-click the server node and, on the shortcut menu, select Configure And Enable Routing And Remote Access. The Routing And Remote Access Server Setup Wizard appears.
5. Click Next to bypass the Welcome page. The Configuration page opens, as shown in Figure 4-12.

FIGURE 4-12 The Configuration page of the Routing and Remote Access Server Setup Wizard

6. Select Custom Configuration and click Next. The Custom Configuration page opens.
7. Select the LAN Routing check box and click Next. The Completing The Routing And Remote Access Server Setup Wizard page opens.
8. Click Finish. A Routing and Remote Access message box appears, prompting you to start the service.
9. Click Start Service.
10. Expand the IPv4 node. Then, right-click the General node and, in the shortcut menu, select New Routing Protocol. The New Routing Protocol dialog box appears.
11. Select DHCP Relay Agent and click OK. A DHCP Relay Agent node appears, subordinate to the IPv4 node.

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NOTE: DHCPV6 RELAY AGENTS
You can also create a relay agent for DHCPv6 by adding a routing protocol to the IPv6 node.

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12. Right-click the DHCP Relay Agent node and, on the shortcut menu, select New Interface. The New Interface For DHCP Relay Agent dialog box appears.
13. Select the interface to the subnet on which you want to install the relay agent and click OK. The DHCP Relay Properties sheet for the interface appears.
14. Leave the Relay DHCP Packets check box selected, and configure the following settings, if needed.
- Hop-Count Threshold Specifies the maximum number of relay agents through which DHCP messages can pass before being discarded. The default value is 4 and the maximum value is 16. This setting prevents DHCP messages from being relayed endlessly around the network.
- Boot Threshold Specifies the time interval (in seconds) that the relay agent should wait before forwarding each DHCP message it receives. The default value is 4 seconds. This setting enables you to control which DHCP server processes the clients for a particular subnet.
15. Click OK.
16. Right-click the DHCP Relay Agent node and, on the shortcut menu, select Properties.
The DHCP Relay Agent Properties sheet appears, as shown in Figure 4-13.

FIGURE 4-13 The DHCP Relay Agent Properties sheet

17. Type the IP address of the DHCP server to which you want the agent to relay messages and click Add. Repeat this step to add additional servers, if necessary.
18. Click OK.
19. Close the Routing And Remote Access console.
At this point, the server is configured to relay DHCP messages to the server addresses you specified.