What is the difference between a subnet mask and a netmask?

Question

Is there any logic in using two different names for determining host ID and net ID?

For example, if you type print route in a Command Prompt you get things with netmask, but the IPv4 settings seems to use subnet mask.

Is there any significant difference between the two terms?

Answer 1

The difference is very, very slight. 9 times out of 10, they will mean the exact same thing.

However, in cases where we're discussing the subnetting of a given network, the two terms "network mask" and "sub-network mask" can have distinct meanings. That is, if we make a distinction between a "network" and a "sub-network" then "the mask of a network" and "the mask of a sub-network" mean different things. In all cases, this distinction is almost purely a relative distinction.

Let's say you've been issued the 10.10.0.0/16 network (using CIDR notation). Here, your "network mask" is 255.255.0.0. Let's say you need to separate this network into 4 smaller networks, each as large as they could possibly be. In order to get 4 networks out of 10.10.0.0/16, you need to borrow two bits (aka, decimal four) from the host address and use them for the subnet addresses. This will give you the following sub-networks:

10.10.0.0/18
10.10.64.0/18
10.10.128.0/18
10.10.192.0/18

Here, your "network mask" is still 255.255.0.0, but each "subnet mask" is 255.255.192.0.

But, as I said, it's completely a relative term. One could also talk about 255.255.192.0 being a "network mask" and then 255.255.0.0 being a "supernet mask". For example, 10.10.0.0/16 is a supernet of, say, 10.10.64.0/18.

Answer 2

The "Netmask", "subnet mask", or simply "mask" are all the same thing: A mask that tells software which IPs belong to that network an which don't.