Changing the Subnet Mask

[Chris]

What advantage/disadvantage would there be in changing the Subnet Mask?

[scuzzman]

It's used in determining the size of, or layers of, your network.

A netmask is a set of four number blocks separated by periods. Each number is normally represented as the decimal equivalent of an eight-bit binary number, which means that each number may take any value between 0 (all eight bits cleared) and 255 (all eight bits set). Every IP address consist of two parts (the network address and the host number). The netmask is used to determine the size of these two parts. The positions of the bits that are set in the netmask are considered to represent the space reserved for the network address, while the bits that are cleared are considered to represent the space set aside for the host number.

[homecomputeraid]

In my opinion, breaking the subnet mask into variable subnets isn't need very often any more. If every PC you have must use a valid Internet Address, and you have several networks to configure, you'll have to split it up using the subnet mask. For home use, I see no advantage to splitting it.

I'd stick mainly to a class 'c' mask of 255.255.255.0 regardless of which private IP scheme you use at home or in a small office.

[edit]To answer your question more succinctly, the left portion of the mask (255.255.255 for example) determines the network portion of an IP address, and the right portion (0 for example) determines which part of the IP is the host address. Does that explain it?

[edit]For a mask of 255.255.255.0, you would be able to use addresses between 1 and 254 for your hosts. So you could use 192.168.1.1 through 192.168.1.254 for host PC's, for example.

Breaking the subnet would allow you to split the hosts you can use into two networks (or more). Your mask would become 255.255.255.128. This would split the network into 2 networks with 126 hosts each. (I know it doesn't add up exactly, but some host IP's (the top and bottom of each subnet) are normally unusable.)

[Scarecrow Man]

the left portion of the mask (255.255.255 for example) determines the network portion of an IP address, and the right portion (0 for example) determines which part of the IP is the host address.

exactly, but I can add to that...

N.N.N.H

8 bits for the host, and 24 bits for the network. This means:

[edit]For a mask of 255.255.255.0, you would be able to use addresses between 1 and 254 for your hosts. So you could use 192.168.1.1 through 192.168.1.254 for host PC's, for example.

2^8 - 2(for network and broadcast addresses (0 and 256)) = 254 hosts