Determining the broadcast address

Installation and Configuration

NameServer and NameServer Load Balancing Details : Understanding server-level and connection-level fault tolerance : Using NameServer replication : Determining the broadcast address

You can determine the broadcast address of a UNIX machine by using the netstat and ifconfig commands, as in the following example:

$ netstat -i
Name Mtu Net/Dest Address Ipkts Ierrs Opkts Oerrs Collis Queue
lo0 8232 loopback localhost 771334 0 771334 0 0 0
le0 1500 bali bali 15069970 286170 10019158 1 302211 0
$ ifconfig le0
le0: flags=863<UP,BROADCAST,NOTRAILERS,RUNNING,MULTICAST> mtu 1500
inet 172.20.0.7 netmask ffff0000 broadcast 172.20.255.255

This example shows that the IP address for bali is 172.20.0.7, and its broadcast address is 172.20.255.255.

To determine the broadcast address in Windows:

1. Enter the ipconfig command in the console, as shown in the following example:

C:\>ipconfig

Windows IP Configuration

Ethernet adapter CE2XPS1:

IP Address. . . . . . . . . : 172.18.103.44
Subnet Mask . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . : 172.18.0.19

2. For each bit in the Subnet Mask that has a value of 0, convert the corresponding bit in the IP Address to 1.

Note that the IP Address and Subnet Mask are composed of four dot-separated decimal numbers and each decimal number represents an 8-bit binary number. Also note that the decimal number 255 is 11111111 in binary.

In this example, the last two decimal digits of the Subnet Mask are zeros. Since the corresponding bits in the IP Address must be converted to 1, the last two decimal numbers of the IP Address should be 255. Therefore the broadcast address is 172.18.255.255. (For more information on determining broadcast addresses, consult with your network administrator.)