The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Network Interface / Internet "Layer Connection" Protocols

TCP/IP Address Resolution For IP Version 6 1 2 3 4 TCP/IP Internet Layer (OSI Network Layer) Protocols

Limitations of RARP

RARP is the earliest and most rudimentary of the class of technologies I call host configuration protocols, which I describe in general terms in a dedicated section. As the first of these protocols, RARP was a useful addition to the TCP/IP protocol in the early 1980s, but has several shortcomings, the most important of which are:

• Low-Level Hardware Orientation: RARP works using hardware broadcasts. This means that if you have a large internetwork with many physical networks, you need an RARP server on every network segment. Worse, if you need reliability to make sure RARP keeps running even if one RARP server goes down, you need two on each physical network. This makes centralized management of IP addresses difficult.
  
  
• Manual Assignment: RARP allows hosts to configure themselves automatically, but the RARP server must still be set up with a manual table of bindings between hardware and IP addresses. These must be maintained for each server, which is again a lot of work on an administrator.
  
  
• Limited Information: RARP only provides a host with its IP address. It cannot provide other needed information such as, for example, a subnet mask or default gateway.

Today, the importance of host configuration has increased since the early 1980s. Many organizations assign IP addresses dynamically even for hosts that have disk storage, because of the many advantages this provides in administration and efficient use of address space. For this reason, RARP has been replaced by two more capable technologies that operate at higher layers in the TCP/IP protocol stack: BOOTP and DHCP. They are discussed in the application layer section on host configuration protocols.

TCP/IP Address Resolution For IP Version 6 1 2 3 4 TCP/IP Internet Layer (OSI Network Layer) Protocols