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An Internet Protocol address (IP address) is a numerical label such as 192.0.2.1 that is assigned to a device connected to a computer network that uses the Internet Protocol for communication. [1] [2] IP addresses serve two main functions: network interface identification, and location addressing.
This means that 256 /8 address blocks fit into the entire IPv4 space. As IPv4 address exhaustion has advanced to its final stages, some organizations, such as Stanford University , formerly using 36.0.0.0 / 8 , have returned their allocated blocks (in this case to APNIC ) to assist in the delay of the exhaustion date.
In the original design of IPv4, an IP address was divided into two parts: the network identifier was the most significant octet of the address, and the host identifier was the rest of the address. The latter was also called the rest field. This structure permitted a maximum of 256 network identifiers, which was quickly found to be inadequate.
An IP address is part of a CIDR block and is said to match the CIDR prefix if the initial n bits of the address and the CIDR prefix are the same. An IPv4 address is 32 bits so an n-bit CIDR prefix leaves 32 − n bits unmatched, meaning that 2 32−n IPv4 addresses match a given n-bit CIDR prefix. Shorter CIDR prefixes match more addresses ...
Since the introduction of CIDR, however, the assignment of an IP address to a network interface requires two parameters, the address and a subnet mask. Given an IPv4 source address, its associated subnet mask, and the destination address, a router can determine whether the destination is on a locally connected network or a remote network.
A wildcard mask is a mask of bits that indicates which parts of an IP address are available for examination. In the Cisco IOS, [1] they are used in several places, for example: To indicate the size of a network or subnet for some routing protocols, such as OSPF. To indicate what IP addresses should be permitted or denied in access control lists ...
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IP packets are composed of a header and payload. The header consists of fixed and optional fields. The payload appears immediately after the header. An IP packet has no trailer. However, an IP packet is often carried as the payload inside an Ethernet frame, which has its own header and trailer.