User's Manual

SPEEDLAN 4100 & 4200 Installation and Operation User Guide
Setting Up the IP Addresses (IP Host Setup) 7-3
Internet Address Classes
The first octet defines the "class" of the address, which is the only method to tell the size of the
network (how big) and where the internet address belongs. There are three main classes:
• Class A: 35.0.0.0
• Class B: 128.5.0.0
• Class C: 192.33.33.0
-non-bolded text = Part of network address
-bolded text = Part of local address (node section)
This definition is not random; it is based on the fact that routers, by reading just the first three bits of
the address field, designate which network class it belongs to. This selection simplifies the way
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