Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

Understanding IP Addressing 93
RULES FOR NETWORK IDS
The following rules apply for creating or using network IDs in a class-based
system:
■ Network IDs cannot begin with 127 as the first octet, since it is reserved for
loopback address.
■ A Network ID cannot have all bits set to 1. This configuration is reserved
for broadcast addresses.
■ A Network ID cannot have all bits set to 0. This configuration is reserved
for indicating a host on the local network.
■ A Network ID must be unique to the IP network.
Table 6.2 lists three network address classes.
RULES FOR HOST IDS
The following rules apply to creating and assigning host IDs:
■ A Host ID cannot have all bits set to 1. This configuration is reserved for
broadcast addresses.
■ A Host ID cannot have all bits set to 0. This configuration is reserved for the
expression of IP network IDs.
■ A Host ID must be unique to the network on which it resides.
Table 6.3 lists host address classes.
Table 6.2
Network Address Classes
Address Class Octets Used First Network ID Last Network ID Number of Networks
Class A 1 1.x.y.z 126.x.y.z 126
Class B 2 128.0.y.z 191.255.y.z 16,384
Class C 3 192.0.0.z 223.255.255.z 2,097152
Table 6.3
Host Address Classes
Address Class Octets Used First Host ID Last Host ID Number of Hosts
Class A 3 w.0.0.1 w.255.255.254 16,777,214
Class B 2 w.x.0.1 w.x.255.254 65,534
Class C 1 w.x.y.1 w.x.y.254 254