Arp protocol port number

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 .

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