Netgear WGR614v3 WGR614v3 Reference Manual - Page 91

Subnet Addressing, Example of Subnetting a Class B Address

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Reference Manual for Cable/DSL Wireless Router WGR614 As a shorter alternative to dotted-decimal notation, the netmask may also be expressed in terms of the number of ones from the left. This number is appended to the IP address, following a backward slash (/), as "/n." In the example, the address could be written as 192.168.170.237/24, indicating that the netmask is 24 ones followed by 8 zeros. Subnet Addressing By looking at the addressing structures, you can see that even with a Class C address, there are a large number of hosts per network. Such a structure is an inefficient use of addresses if each end of a routed link requires a different network number. It is unlikely that the smaller office LANs would have that many devices. You can resolve this problem by using a technique known as subnet addressing. 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. Class B Network Subnet Node 7262 Figure 7-2: 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 172.16.0.0 is assigned, but node addresses are limited to 255 maximum, allowing eight extra bits to use as a subnet address. The IP address of 172.16.97.235 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 organization. Network, Routing, Firewall, and Basics B-5

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Reference Manual for Cable/DSL Wireless Router WGR614
Network, Routing, Firewall, and Basics
B-5
As a shorter alternative to dotted-decimal notation, the netmask may also be expressed in terms of
the number of ones from the left. This number is appended to the IP address, following a backward
slash (/), as “/n.” In the example, the address could be written as 192.168.170.237/24, indicating
that the netmask is 24 ones followed by 8 zeros.
Subnet Addressing
By looking at the addressing structures, you can see that even with a Class C address, there are a
large number of hosts per network. Such a structure is an inefficient use of addresses if each end of
a routed link requires a different network number. It is unlikely that the smaller office LANs would
have that many devices. You can resolve this problem by using a technique known as subnet
addressing.
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 7-2:
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 172.16.0.0 is assigned, but node addresses are limited to 255 maximum, allowing
eight extra bits to use as a subnet address. The IP address of 172.16.97.235 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
organization.
7262
Class B
Network
Subnet
Node