IP addressing and Subnetting workbook

Every networking student should have a solid understanding of TCP/IP subnetting (Loshin, 1997). Subnetting’s importance in modern networking is reflected by its many and varied uses. It can enhance network performance by splitting up collision and broadcast domains in a routed network (Odom, 2000). Large networks can be organized into separate subnets representing departmental, geographical, functional, or other divisions (Feit, 1997). Since hosts on different subnets can only access each other through routers, which can be configured to apply security restrictions, subnetting can also serve as a tool for implementing security policies (Bulette, 1998). Dividing a large network into subnets and delegating administrative responsibility for each subnet can make administration of a large network easier. Routers can require that a WAN link connecting two networks must itself form a separate subnet (Bulette, 1998). Troubleshooting, diagnosing, and fixing problems in a TCP/IP internetwork typically require thorough familiarity with subnetting. Network design requires both the ability to understand and carry out subnetting.

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Subnetting Principles

Subnetting lets you borrow bits from the host and use them to allow for more networks. When subnetting, separating the network and host requires a special mechanism called a subnet mask. A subnet mask, which contains a binary bit pattern of ones and zeros, is applied to an address to extract the network ID for purposes of determining whether an address is on the local network. If not, the address is switched or routed on.

The function of a subnet mask is to extract the network ID portion of an IP destination address and determine whether an IP address exists on the local network or whether it must be routed outside the local network. If the extracted network ID matches the local network ID, the destination is located on the local network. However, if they don't match, the message must be routed outside the local network. The process used to apply the subnet mask involves Boolean algebra to filter out nonmatching bits.

 

IP Subnetting

Visual ip subnettingA subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.Subnet MaskPerhaps the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation.