It's valid and it's called a noncontiguous subnet mask since the 16 bits for
the subnet mask are not contiguous. The RFC's, however, recommend against
using noncontiguous subnet masks.
According to the standard RFC3021 (IETF):
Using a 31-bit prefix length leaves only two numbering possibilities (see Section 2.1), eliminating the use of a directed broadcast to the link (see Section 2.2.1). The limited broadcast MUST be used for all broadcast traffic on a point-to-point link with a 31-bit subnet mask assigned to it.
So it is a valid netmask for point-to-point networks only, but this is an exception: for other netmasks, the first and last address in any range are reserved (network address and broadcast address).
However you can't use 255.255.255.254 as a netmask on Windows machines, since Microsoft guys didn't read the spec (or they considered you cannot do a point-to-point connection with your computer). So on those machines, the highest mask would be 255.255.255.252, using 30 mask bits resulting in 2 usable addresses + one broadcast address + one address representing the network.
Yes. The subnet mask of 255.255.0.0 (/16) is used in the Class B network of 172.16.0.0.
It does not require a subnet mask.
If this is a default subnet mask, then it would be a class C subnet mask. If you are subnetting a network and this is not the default subnet mask, then it could be either a class A or class B.
The default subnet mask has a standard size. The custom subnet mask allows you to make subnets that are smaller or larger than the default.
The correct term is subnet mask instead of subnet mass. A subnet mask separates an IP address into the host address and the network address. It is a 32-bit number that can mask an IP address.
2 given subnets
255.255.255.0
255.255.255.0
Subnet mask for the above is 255.0.0.0
if the ip address is 192.168.2.1 then the subnet mask should be 255.255.255.0
The default subnet mask would be 255.255.0.0 for a class B address.
By changing subnet mask..from 255.255.224.0 to 255.255.240.0 Number of subnetworks increase and the number of host in each subnetwork decreases
It depends on whether you are subnetting or not. If not, the default subnet mask would be 255.255.255.0