Avaya Configuring IP, ARP, RARP, RIP, and OSPF Services Manuel d'utilisateur télécharger pdf (Page 87)

Configuring and Customizing IP

308627-14.20 Rev 00

3-27

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 ones or

all zeros in the host portion.

For example, the IP Class A 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 ones or all

zeros, the broadcast address for that network could be 10.255.255.255 or

10.0.0.0, 255.255.255.255.

You configure a broadcast address for a subnet differently 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 10.4.255.255. An alternative broadcast address is 10.4.0.0.

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 ones in the host portion.

Accept the default value unless the calculated broadcast address (host portion) of

all ones is not adequate. In this case, use the BCC or Site Manager to enter the

appropriate IP broadcast address in dotted-decimal notation.

Using the BCC

To specify a broadcast address, go to an IP interface prompt (for example,

stack;

eth 2/2/2; ip/2.2.2.2/255.255.0.0

) and enter:

broadcast

<broadcast_address>

broadcast_address

is an IP address expressed in dotted-decimal notation.

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Avaya Configuring IP, ARP, RARP, RIP, and OSPF Services Manuel d'utilisateur Page 87