Cisco Systems 78-11741-02 manual Class Address or Range Status

Configuring IP Addressing

Assigning IP Addresses to Network Interfaces

Table 3	Reserved and Available IP Addresses
Class		Address or Range	Status
A		0.0.0.0	Reserved
		1.0.0.0 to 126.0.0.0	Available
		127.0.0.0	Reserved
B		128.0.0.0 to 191.254.0.0	Available
		191.255.0.0	Reserved
C		192.0.0.0	Reserved
		192.0.1.0 to 223.255.254	Available
		223.255.255.0	Reserved
D		224.0.0.0 to 239.255.255.255	Multicast group addresses
E		240.0.0.0 to 255.255.255.254	Reserved
		255.255.255.255	Broadcast

The official description of IP addresses is found in RFC 1166, Internet Numbers.

To receive an assigned network number, contact your Internet service provider (ISP).

An interface can have one primary IP address. To assign a primary IP address and a network mask to a network interface, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# ip address ip-address mask	Sets a primary IP address for an interface.

A mask identifies the bits that denote the network number in an IP address. When you use the mask to subnet a network, the mask is then referred to as a subnet mask.

Note We only support network masks that use contiguous bits that are flush left against the network field.

The tasks to enable or disable additional, optional, IP addressing features are contained in the following sections:

•Assigning Multiple IP Addresses to Network Interfaces

•Enabling Use of Subnet Zero

•Disabling Classless Routing Behavior

•Enabling IP Processing on a Serial Interface

Cisco IOS IP Configuration Guide

IPC-8