No subnet
No subnet mark law
For non-subnet IP address, host number can be written as a mask to zero. Such as the IP address 210.73.140.5, mask is 255.255.255.0, the default mask can also write only the IP address.
Subnets
There subnet mark law
When subnets, be sure to pair both appeared. To Class C address, for example.
The following is a specified mask 27 (1111 1111, 1111 1111, 1111 1111, 1110 0000 => 255.255.255.224
1. IP address in the previous network number represented by 3 bytes, the bytes can indicate a subnet number, and host number explained further described two IP addresses belong to the same network segment. If you belong to the same network range, the exchange of information between the two addresses is not through a router. If it does not belong to the same network range, which is different subnet number, information exchange two addresses will be carried out through a router.
E.g:
For the IP address of 210.73.140.5 host, the host identifies that 5 => 00000101,
For the IP address of the host 210.73.140.16 is identified as its host 16 => 00010000,
Two or three front host identifier 000 is full, indicating that the two IP addresses, the two hosts need not be the same router when the exchange network area information.
Host Identity is 210.73.60.1 1 => 00000001,
Host Identity is 210.73.60.252 = 252> 11111100,
In front of these two host identifier 000 and three 111 are different, then the two different areas of the network, routers need to exchange information. Its subnet host number 1 each and 252.
2. There is a function of the subnet mask and there are several subnets, but the number of subnets can be expressed as a range, not exactly speak several specific subnet mask does not explain the specific subnet number format subnet mask (class C address).