Subnet mask

The subnet mask is subject to the control of the network administrator, and specifies the structure of the subnet.

Small networks without a router do not require a subnet mask. The same is true if you do not use registered IP numbers. A subnet mask can be used to subdivide the network with the aid of the mask instead of using a large number of network numbers.

The subnet mask is a 32-bit number.

  • Ones in the mask indicate the subnet part of an address region.
  • Zeros indicate that part of the address region which is available for the host IDs.

Description

Binary representation

Decimal representation

IP address

10101100.00010000.00010001.11001000

172.16.17.200

Subnet mask

11111111.11111111.00010100.00000000

255.255.20.0

Network ID

10101100.00010000.00010000.00000000

172.16.16.0

Host ID

00000000.00000000.00000001.11001000

0.0.1.200

Standard subnet mask

Address class

Standard subnet mask (decimal)

Standard subnet mask (hex)

A

255.0.0.0

FF.00.00.00

B

255.255.0.0

FF.FF.00.00

C

255.255.255.0

FF.FF.FF.00

 

Note

Neither subnet 0 nor the subnet consisting only of ones may be used. Neither host number 0 nor the host number consisting only of ones may be used! If the IP address is set using the KS2000 configuration software, it is necessary for the subnet mask also to be changed with the KS2000 configuration software. If ARP addressing is used, the associated standard subnet mask, based on the IP address, is entered. Under BootP or DHCP the subnet mask is entered by the server.