broadcast address

broadcast address

An address that enables transmission to every node in a local network. The address is the highest numeric value of the address format being used. An Ethernet broadcast address is all binary 1's. An IP broadcast address is the highest number in its class; for example, the broadcast address of a Class C 192.168.16.0 network is 192.168.16.255.

Subnet Broadcast Addresses
The broadcast address for a subnet must account for the part of the address that is reserved for the subnet. Using the above Class C example configured for six subnets would have a broadcast address of 192.168.16.31. It is derived as follows. For more on the Class C example, see subnet mask. See broadcast and multicast.

 Class C Mask for Six Subnets

   255      255      255    224
 11111111.11111111.11111111.11100000

 Step 1
 Invert the mask.

    0        0        0           31
 00000000.00000000.00000000.00011111

 Step 2
 OR the inverted mask with an IP
 address in the subnet, such as
 192.168.16.1.

 192       168        16           1
 11000000.10101000.00010000.00000001 
 00000000.00000000.00000000.00011111
 -----------------------------------
 11000000.10101000.00010000.00011111
 192       168        16          31