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HOMEWORK NETW110: Edwige Annie Robinson d02052430

Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you don't subnet, you will only be able to use one network from your Class A, B, or C network. Unless you have been assigned many major networks, you really need to subnet.

Each data link on a network must be a unique subnet, with every node on that link being a member of the same subnet. For serial interfaces (standard HDLC), you will need one subnet for the circuit, or "wire" (both ends of the serial connection will be in the same subnet). If you are planning on implementing Frame Relay, SMDS, X.25 etc, read the Router Products Configuration and Reference Guides for assistance in configuring.

A subnet mask is defined for each IP address. The subnet mask identifies which portion of the 4 octets is used to identify the data link, with the remaining bits identifying the node. If you want no subnetting, use these default masks (255 - strictly follow number, 0 - wildcard):

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0

Let's use these two addresses for some examples: 171.68.3.3 and 171.68.2.3. If the subnet mask is 255.255.255.0, the first 24 bits are masked, so the router compares the first 3 octets of the two addresses. Since the masked bits are not the same, the router knows that these addresses belong to different subnets.

If the subnet mask is 255.255.0.0, the first 16 bits are masked, so the router compares the first 2 octets of the two addresses. Since the masked bits are the same, the router knows that these addresses belong to the same subnet.

Nodes and routers use the mask to identify the data link on which an address resides. For instance, imagine that San Francisco proper is a class B network, and think of the streets as subnets. Each street must have a unique name. How would the postal service deliver a letter or find the correct destination if there were two Lombard Streets? Each house number can