
Configuring IP Services
3-16 114065 Rev. A
Specifying a Broadcast Address for an Interface
In broadcasting, the IP router transmits a single packet to every host on an
attached network. To do so, it uses a broadcast address that refers to all hosts on
the network. A broadcast address is simply an IP address that contains all 1s or all
0s in the host portion.
For example, the IP Class C address 10.3.45.12 has the following characteristics:
• Because the address is for a Class A network (the network portion is 1 byte),
the host portion contains 3 bytes.
• Because the host portion of a broadcast address consists of all 1s or all 0s, the
broadcast address for that network can be one of the following:
10.255.255.255, 10.0.0.0, 255.255.255.255, or 0.0.0.0.
Some networks do not support broadcasts; thus, configuring an IP broadcast
address does not guarantee efficient broadcast delivery.
By default, IP uses a broadcast address that contains all 1s in the host portion.
You can use Site Manager to configure a broadcast address on an IP interface.
Accept the default, 0.0.0.0, unless the calculated broadcast address (host portion)
of all 1s is not adequate. If this is the case, then enter the appropriate IP broadcast
address in dotted decimal notation.
Specifying a Subnet Broadcast Address
The way you configure a broadcast address for a subnet is different from the way
you configure a broadcast address for a network. When you extend the network
portion of the IP address to create a subnet address, you automatically take away
from the host portion of the address. To configure a subnet broadcast, you take the
subnet mask for that subnet and invert it. For example, if the IP address of the
subnet is 10.4.2.3, and the mask is 255.255.0.0, then the subnet broadcast address
is either 10.4.255.255 or 10.4.0.0.
Site Manager: Broadcast Address parameter: page A-25.
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