What is a Subnet mask?

Answer 1

The word subnetwork (usually shortened to subnet) has two related meanings. In the older and more general meaning, it meant one physical network of an internetwork. In the internet Protocol (IP), a subnetwork is a division of a classful network. The rest of this article is about the second meaning. Subnetting an IP network allows a single large network to be broken down into what appear (logically) to be several smaller ones. It was originally introduced before the introduction of classful network numbers in IPv4, to allow a single site to have a number of local area networks. Even after the introduction of classful network numbers, subnetting continued to be useful, as it reduced the number of entries in the Internet-wide routing table (by hiding information about all the individual subnets inside a site). As a side benefit, it also resulted in reduced network overhead, by dividing the parts which receive IP broadcasts.

Answer 2

subnet maskis the network address plis the bit reseived to identfying subnetworking. a mask used to determine what subnet an IP address belongto.An IP address has two components, the network address and the host address. sub netting enables the network administrator to futher divde the host part of the address into two or more subnet.

Answer 3

The subnet mask is used by the Internet Protocol (IP) addressing scheme to determine if a packet of data is destined to a local or non-local network address. It is called a mask because it is used to to "mask" bits to determine if an address is on the same network. Masking is done by the Boolean bit logic "AND," where "1 AND 1" is a "1," and "0 AND 1," "1 AND 0," and "0 AND 0" all produce a "0."

In simple programming, an IP address is in the same network if, and only if:

"My IP & Subnet Mask" = "Other IP & Subnet Mask".

For simplicity, consider the address 10.0.0.5 with a subnet mask of 255.0.0.0. Performing the "mask" operation yields a base network IP "address" of 10.0.0.0. Note that you can't actually communicate with this IP address, because it represents the entire network.

If two other computers have the address 65.25.10.12 and 10.34.98.123, the respective masking operations using 255.0.0.0 will yield the networks 65.0.0.0 and 10.0.0.0; the computer can immediately tell that the first IP address isn't on the local network, but the second one is.

If a computer is configured with the wrong subnet mask or IP address, it will be unable to communicate with some or all of the computers on the network. As in the previous example, if the computer with the address 10.34.98.123 had a subnet mask of 255.255.0.0, it would be unable to communicate with 10.0.0.5, because it would try to send that IP through the gateway, which the gateway would reject since it is a local IP address.

Similarly, if the computer were changed to 65.1.2.12 mask 255.0.0.0, it would be unable to communicate with any device on the 10.0.0.0 network nor the outside world, because the default gateway would be outside of its own network.

Answer 4

A subnet mask is a number that defines a range of IP addresses that can be used in a network. A common subnet mask for a Class C IP address is 255.255.255.0.