Posted by arlene

The Windows 2000/2003 DHCP servers provide support for BOOTP clients. The Default BOOTP user class of options is used to configure the information that is supplied to these clients. Although standard BOOTP servers require that the server be configured in advance with a table of client hardware addresses and corresponding IP addresses, Windows 2000/Server 2003 DHCP servers instead select the next available address to give to a BOOTP client. This matches the method the DHCP server useswhen granting IP address leases to its DHCP clients.

Enabling the DHCP Relay Agent

RFC 1542, “Clarifications and Extensions for the Bootstrap Protocol,” defined support for a BOOTP relay agent. That agent now is supported by almost every router. The relay agent function enables you to support clients on different subnets using a single BOOTP or DHCP server. DHCP requests are forwarded by the router to the DHCP server, and the server’s responses are returned to the client. Because BOOTP and DHCP use almost the same frame format and the same UDP ports, you’ll also find that most BOOTP relay agents will perform this duty for DHCP clients.

However, on a small network, you might not have a router. Instead, you might be using the Routing and Remote Access services available in Windows 2000/2003 Servers. In that case, you’ll need to add the DHCP Relay Agent protocol. Follow these steps to enable the DHCP Relay Agent:

1. Click Start, Programs, Administrative Tools (Start, Administrative Tools for 2003), and then Routing and Remote Access (for Windows Server 2003, Start, Administrative Tools, Routing and Remote Access).
2. In the left pane of the MMC console utility, click the plus sign to expand the server’s list of objects.
3. Click the plus sign for IP Routing to expand the list of objects it contains.
4. Right-click on General, and from the menu that pops up select New Routing Protocol.
5. You can see the New Routing Protocol dialog box displaying a list of available protocols. Select DHCP Relay Agent, and click OK to dismiss the dialog box. The DHCP Relay Agent protocol now shows up as an object under IP Routing.
6. Right-click on this new object and select Properties. In the Properties sheet for the DHCP Relay Agent, you can add the addresses of one or more DHCP servers to which BOOTP and DHCP messages will be relayed.

When the relay agent receives a DHCP or BOOTP broadcast message on one of its network interfaces, which it can recognize because the packet is addressed to port 67, it will forward the message to a DHCP server. The DHCP server resides on Subnet 1 along with other servers. This subnet is connected to Subnet 2 using a router—or possibly a Windows 2000 server running the DHCP Relay Agent service.

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