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Configuring IP addressing
The IP addresses in this chapter refer to IPv4 addresses unless otherwise specified.
This chapter describes IP addressing basics and manual IP address assignment for interfaces.
Dynamic IP address assignment (BOOTP and DHCP) and PPP address negotiation are beyond the
scope of this chapter.
Overview
This section describes the IP addressing basics.
IP addressing uses a 32-bit address to identify each host on an IPv4 network. To make addresses
easier to read, they are written in dotted decimal notation, each address being four octets in length.
For example, address 00001010000000010000000100000001 in binary is written as 10.1.1.1.
IP address classes
Each IP address breaks down into the following sections:
• Net ID—Identifies a network. The first several bits of a net ID, known as the class field or class
bits, identify the class of the IP address.
• Host ID—Identifies a host on a network.
IP addresses are divided into five classes, as shown in Figure 11. The shade
d areas represent the
address class. The first three classes are most commonly used.
Figure 11 IP address classes
Table 1 IP address classes and ranges
Class Address range Remarks
A 0.0.0.0 to 127.255.255.255
The IP address 0.0.0.0 is used by a host at startup for
temporary communication. This address is never a
valid destination address.
Addresses starting with 127 are reserved for loopback
test. Packets destined to these addresses are
processed locally as input packets rather than sent to
the link.
B 128.0.0.0 to 191.255.255.255 N/A
C 192.0.0.0 to 223.255.255.255 N/A
D 224.0.0.0 to 239.255.255.255 Multicast addresses.
E 240.0.0.0 to 255.255.255.255
Reserved for future use, except for the broadcast
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