Avaya Configuring IP Services Bedienungsanleitung PDF herunterladen (Seite 35)

Configuring IP Routers and Interfaces

2-7

Specifying a Broadcast Address

Broadcasting occurs when 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, if you have an IP network with IP address 10.3.45.12, you can

conﬁgure a broadcast address for that network, as follows:

• 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.

Subnet Broadcast Addresses

The way you conﬁgure a broadcast address for a subnet is different from the way

you conﬁgure a broadcast address for a network. Because you extend the network

portion of the IP address when you create subnets, you automatically take away

from the host portion of the IP 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.

IP permits an all-zero subnet address but discourages its use for the following

reason. If an all-zero subnet address and an all-zero broadcast address are both

valid, the router cannot distinguish an all-subnets broadcast from a directed

broadcast for the zero subnet.

For instructions on using Site Manager to conﬁgure a broadcast address on an IP

interface, see the Broadcast Address parameter on page 2-38.

For information on using Site Manager to allow the use of an all-zero subnet address, see

the Zero Subnet Enable parameter on page 2-59.

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Avaya Configuring IP Services Bedienungsanleitung Seite 35