Sub Net Mask example essay topic

HOMEWORK NETW 110: Edw ige Annie Robinson d 02052430 Sub netting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you don't sub net, 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 sub net. Each data link on a network must be a unique sub net, with every node on that link being a member of the same sub net. For serial interfaces (standard HDLC), you will need one sub net for the circuit, or 'wire' (both ends of the serial connection will be in the same sub net). 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 sub net mask is defined for each IP address. The sub net 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 sub netting, 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 sub net 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 sub nets. 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 sub net.

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 sub nets. 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 be thought of as a unique identifier for that street.

The house numbers themselves can be duplicated on other streets: 33 Market Street is not the same as 33 Van Ness Avenue. San Francisco. Lombard. 33171.68. 3.3 San Francisco. Market.

33171.68. 2.3 Sometimes you need to perform a logical 'AND' operation to find out what sub net your node is in. Performing an 'AND' operation means that anytime you 'AND' a 0 value to another 0 or a 1 value, the result is 0. Only a 1 AND ed with another 1 value will result in a 1 value. Here's how it works: 0 AND 0 IS 00 AND 1 IS 01 AND 1 IS 1 Let's compare our sample addresses (171.68. 3.3 and 171.68.

2.3) against the sub net mask 255.255. 240.0. We need to compare the binary representation of the third octet of the mask with the binary representation of the third octets of the addresses. In order to do this, we " ll perform a logical 'AND' operation on the corresponding bits in each octet. The masked bits are those that are 'turned on,' or 1 in the mask. Since the masked bits in both addresses are the same, the router knows that these addresses belong to the same sub net..