D-Link DES-3326S manual Calculating the Number of Subnets and Nodes

DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

The Default subnet masks are:

•Class A – 11111111.00000000.00000000.00000000 255.0.0.0

•Class B – 11111111.11111111.00000000.00000000 255.255.0.0

•Class C – 1111111.11111111.11111111.00000000 255.255.255.0

Additional bits can be added to the default subnet mask for a given Class to further subnet a network. When a bitwise logical AND operation is performed between the subnet mask and the IP address, the result defines the Subnet Address.

Some restrictions apply to subnet addresses. Addresses of all “0”s and all “1”s are reserved for the local network (when a host does not know it’s network address) and for all hosts on the network (the broadcast address). This also applies to subnets. A subnet address cannot be all “0”s or all “1”s. A 1-bit subnet mask is also not allowed.

Calculating the Number of Subnets and Nodes

To calculate the number of subnets and nodes, use the formula (2n – 2) where n = the number of bits in either the subnet mask or the node portion of the IP address. Multiplying the number of subnets by the number of nodes available per subnet gives the total number of nodes for the entire network.

Example

00001010.00101010.01001001.11010010 10.42.73.210 Class A IP address

11111111.11100000.00000000.00000000 255.224.0.0 Subnet Mask

00001010.00100000.00000000.00000000 10.32.0.0 Network Address

00001010.00101010.11111111.11111111 10.32.255.255 Broadcast Address

Switch Management and Operating Concepts 85