Sub netting

Subnetting

Sub-netting is a process of breaking the network into smaller units. These units can be called subnets. Each subnet is a non-physical description(ID) for a physical sub-network.

Benefits of Sub netting

• Reduce network traffic.
• Reduce the size of the routing table.
• Simplified Management: It’s easier to identify and isolate network problems in a group of smaller connected networks than within one gigantic network.
• Optimized network performance: This is a result of reduced network traffic.
• It also increases security of the network and helps contain network traffic to local network segments.

With sub-netting, the number of segments increases, while the number of hosts in each segment reduces. For example, consider a network with an IP address of 192.168. 2.0. With the default subnet mask of 255.255.255.0, you can have only one large network segment with 254 hosts. If you use some bits from the host portion, you can create two, three, or four segments. But as the number of segments increases, the number of hosts in each segment reduces.

Implementing Sub netting

Before implementation, we can determine some requirement and plans to best implement your subnet scheme.

• Determine the number of required network IDs
       -One for each subnet
       -One for each wide-area network connection.
• Determine the number of required host IDs per subnet
       -One for each TCP/IP host
       -One for each router interface
• Define one subnet mask based on requirements.
• Define a unique subnet ID for each physical segment based on the subnet mask.
• Define valid host IDs for each subnet based on the subnet ID.

Subnet Mask

Subnet mask is a 4 byte (32 bits) number used to identify the sub-network ID and the host ID from an IP address. Every class of the IP address uses the different range of the sub-network. Subnet mask allow the IP based networks to be divided into the sub network, i.e, 255.255.255.0, 255.255.170.0. Table shows the default subnet mask of class A,B, and C.