NETGEAR ME103 User Manual

Page 87

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Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

Network, Routing, Firewall, and Cabling Basics


August 2003

Subnet addressing allows us to split one IP network address into smaller multiple physical
networks known as subnetworks. Some of the node numbers are used as a subnet number instead.
A Class B address gives us 16 bits of node numbers translating to 64,000 nodes. Most
organizations do not use 64,000 nodes, so there are free bits that can be reassigned. Subnet
addressing makes use of those bits that are free, as shown below.

Figure 6-4: Example of Subnetting a Class B Address

A Class B address can be effectively translated into multiple Class C addresses. For example, the
IP address of is assigned, but node addresses are limited to 255 maximum, allowing
eight extra bits to use as a subnet address. The IP address of would be interpreted as
IP network address 172.16, subnet number 97, and node number 235. In addition to extending
the number of addresses available, subnet addressing provides other benefits. Subnet addressing
allows a network manager to construct an address scheme for the network by using different
subnets for other geographical locations in the network or for other departments in the

Although the preceding example uses the entire third octet for a subnet address, note that you are
not restricted to octet boundaries in subnetting. To create more network numbers, you need only
shift some bits from the host address to the network address. For instance, to partition a Class C
network number ( into two, you shift one bit from the host address to the network
address. The new netmask (or subnet mask) is The first subnet has network
number with hosts to, and the second subnet has
network number with hosts to


The number is not assigned because it is the broadcast address

of the first subnet. The number is not assigned because it is the network
address of the second subnet.


Class B