DHCP for Windows 2000

Chapter 2. In The Beginning: RARP and BOOTP

This chapter describes the predecessors to DHCP, the Reverse Address Resolution Protocol (RARP) and the Bootstrap Protocol (BOOTP). These two protocols are illustrated here to highlight the need for a more robust and dynamic configuration protocol as well as to provide a basic foundation to understanding DHCP.

RARP

RARP is a protocol that exists at the Data Link Layer. Think of it as the exact opposite of ARP (described in Chapter 1). It provides a mechanism for a host to determine its IP address when it is only aware of its MAC address.

RARP typically is utilized when a diskless workstation is booted. Since it does not have any IP configuration data stored locally, it must use RARP to find out its IP address. RARP accomplishes this by using a client/server process. The RARP server contains a database that simply maps IP addresses to their corresponding MAC addresses.

When a RARP client wants to find out its IP address, it sends a broadcast Ethernet frame (target MAC address = FF:FF:FF:FF:FF:FF) containing its MAC address. The RARP server, upon receiving the message, looks up the requester’s MAC address in its RARP table. If a match is found, the RARP server creates a reply packet that contains the requester’s IP address (see Figure 2.1). If no match is found, the packet is discarded.

Figure 2-1. Example of RARP

Although very basic in functionality, ...