User's Manual

SPEEDLAN 9000 Installation and Operation User Guide
Basics of IP Addressing 5-3
This definition is not random; it is based on the fact that units/routers, by reading just the first three
bits of the address field, designate which network class it belongs to. This selection simplifies the way
units/routers handle the messages (packets) and speed up the forwarding process.
In fact, IP defines five classes:
•
Class A addresses use 8 bits (1 octet) for the network portion and 24 bits (3 octets) for the
node (or host) section of the address. This provides up to 128 networks with 16.7 million
nodes for each network.
• First byte is assigned as network address
• Remaining bytes used for node addresses
• Format: network, node, node, node
• In IP address 49.22.102.70, "49" is network address and "22.102.70" is the node
address—all machines on this network have the "49" network address assigned to them
• Maximum of 224 or 16,777,216 nodes
• Class B addresses use 16 bits (two octets) for the network portion and 16 bits for the node
(or host) section of the address. This provides up to 16, 384 networks with 64,534 nodes
for each network.
• First two bytes are assigned as network address
• Remaining bytes used for node addresses
• Format: network, network, node, node
• In IP address 130.57.30.56, "130.57" is the network address, and "30.56" is the node
address
• Maximum of 216 or a total of 65,534 nodes
• Class C addresses use 24 bits (3 octets) for the network portion and 8 bits (two octets) for
the node (or host) section of the address. This provides 16.7 million networks with 256
nodes for each network.
• First three bytes are assigned as network address
• Remaining byte used for node address
• Format: network, network, network, node
• In IP address 198.21.74.102, "198.21.74" is the network address, and "102" is the
node address
• Maximum of 28 or 254 node addresses