Installing and Administering LAN/9000 Software

140 Chapter6

Network Addressing

Subnet Addresses

Subnetting is an optional addressing scheme that allows you to partition

the host address portion of an internet address into discrete

subnetworks. This allows you to have multiple physical networks

without requiring you to obtain multiple network addresses. The

physical networks are connected via gateways.

For example, if you have a large installation with many interconnected

nodes, you could run into hardware conﬁguration restrictions or

performance degradation if you tried to place all nodes on the same

physical network. With subnetting you can install several smaller

physical networks but have them all share the same network address.

When messages with subnet addresses are routed across the network,

the internet address is ANDed with the subnet mask to determine the

subnetwork address. (0 values in the subnet mask convert corresponding

bits in the IP address to 0.)

Figure 6-5 shows how a Class C Internet address and a subnet mask

combine to form a subnet address.