Class A Addresses
Class A address must be between 0 and 127
Class B Addresses
Class A address must be between 128 and 191
Class C Addresses
Class A address must be between 192 and 223
Network Addresses: Special Purpose
Some IP addresses are reserved for special purposes, so network administrators can’t ever assign these addresses to nodes.
Network address of all 0s -- Interpreted to mean “this network or segment.”
Network address of all 1s -- Interpreted to mean “all networks.”
Network 127.0.0.0 -- Reserved for loopback tests. This address designates the local node and allows that node to send a test packet to itself without generating network traffic.
Node address of all 0s -- Interpreted to mean “network address” or any host on a specified network.
Node address of all 1s -- Interpreted to mean “all nodes” on the specified network;for example, 18.104.22.168 means all nodes on network 128.2 (which is a Class B address).
Entire IP address set to all 0s -- Used by Cisco routers to designate the default route.This address could also mean “any network.”
Entire IP address set to all 1s -- (same as 255.255.255.255) Broadcast to all nodes on the current network;sometimes called an all 1s broadcast or a limited broadcast.