Cisco Systems 78-11741-02 Helper Addresses Example, Flooding of IP Broadcasts Example, IPC-60

Configuring IP Addressing

IP Addressing Examples

A directed broadcast address includes the network or subnet fields. For example, if the network address is 128.1.0.0, the address 128.1.255.255 indicates all hosts on network 128.1.0.0, which would be a directed broadcast. If network 128.1.0.0 has a subnet mask of 255.255.255.0 (the third octet is the subnet field), the address 128.1.5.255 specifies all hosts on subnet 5 of network 128.1.0.0—another directed broadcast.

Flooding of IP Broadcasts Example

In the following example, flooding of IP broadcasts is enabled on all interfaces (two Ethernet and two serial). No specific UDP protocols are listed by a separate ip forward-protocol udp interface configuration command, so the default protocols (TFTP, DNS, Time, NetBIOS, and BOOTP) will be flooded.

ip forward-protocol spanning-tree bridge 1 protocol dec

access-list 201	deny 0x0000 0xFFFF
interface ethernet 0
bridge-group 1
bridge-group 1	input-type-list 201
bridge-group 1	input-lsap-list 201
interface ethernet 1
bridge-group 1
bridge-group 1	input-type-list 201
bridge-group 1	input-lsap-list 201
interface serial 0
bridge-group 1
bridge-group 1	input-type-list 201
bridge-group 1	input-lsap-list 201
interface serial 1
bridge-group 1
bridge-group 1	input-type-list 201
bridge-group 1	input-lsap-list 201

Helper Addresses Example

In the following example, one router is on network 192.168.1.0 and the other is on network 10.44.0.0, and you want to permit IP broadcasts from hosts on either network segment to reach both servers. Figure 13 illustrates how to configure the router that connects network 10.44.0.0 to network 192.168.1.0.

Cisco IOS IP Configuration Guide

IPC-60