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Table Of Contents  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
           9  Address Resolution and the TCP/IP Address Resolution Protocol (ARP)

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Dynamic Address Resolution Caching and Efficiency Issues
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ARP Overview, Standards and History
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TCP/IP Address Resolution Protocol (ARP)

The most widely used network layer protocol in the world—by far—is the TCP/IP Internet Protocol. It's no surprise then, that the most important address resolution protocol is the TCP/IP protocol bearing the same name as the technique itself: the Address Resolution Protocol (ARP). ARP is a full-featured dynamic resolution protocol used to match IP addresses to underlying data link layer addresses. Originally developed for Ethernet, it has now been generalized to allow IP to operate over a wide variety of layer two technologies.

In this section I describe the operation and features of ARP. I begin with an overview of the protocol, and a discussion of its defining standards and history. I briefly outline how addresses are specified in ARP and its general operation, as well as describing the message format used for ARP messages. I then turn to the important matter of caching in ARP and how that is used to improve performance. I conclude with a discussion of proxying in ARP, which is needed to support special network connectivity situations.

Background Information: The general explanation of address resolution, what it is, and how it works, can be found in the preceding section on address resolution concepts. Except for a brief recap at the start of the overview, I assume you have familiarity with these concepts.


Note: The Address Resolution Protocol described here is used for resolving unicast addresses in version 4 of the Internet Protocol. Multicast addresses under IPv4 use a direct mapping method, described in a separate topic. IPv6 uses the new Neighbor Discovery protocol instead of ARP; this is discussed in the overview of IPv6 address resolution.


Related Information: For a discussion of ARP-related issues in networks with mobile IP devices, see the section on Mobile IP.


Related Information: The software application “arp”, which is used to administer the TCP/IP ARP implementation on a host, is covered in its own topic in the section on TCP/IP utilities.


Quick navigation to subsections and regular topics in this section



Previous Topic/Section
Dynamic Address Resolution Caching and Efficiency Issues
Previous Page
Pages in Current Topic/Section
1
Next Page
ARP Overview, Standards and History
Next Topic/Section

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