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Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-09
Chapter 31 Configuring IP Unicast Routing
Configuring IP Addressing on Layer 3 Interfaces
If you do not specify any UDP ports when you configure the forwarding of UDP broadcasts, you are
configuring the router to act as a BOOTP forwarding agent. BOOTP packets carry Dynamic Host
Configuration Protocol (DHCP) information.
Beginning in privileged EXEC mode, follow these steps to enable forwarding UDP broadcast packets on
an interface and specify the destination address:
Use the no ip helper-address interface configuration command to disable the forwarding of broadcast
packets to specific addresses. Use the no ip forward-protocol global configuration command to remove
a protocol or port.
Establishing an IP Broadcast Address
The most popular IP broadcast address (and the default) is an address consisting of all ones
(255.255.255.255). However, the switch can be configured to generate any form of IP broadcast address.
Beginning in privileged EXEC mode, follow these steps to set the IP broadcast address on an interface:
To restore the default IP broadcast address, use the no ip broadcast-address interface configuration
command.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Enter interface configuration mode, and specify the Layer 3 interface
to configure.
Step 3
ip helper-address address
Enable forwarding and specify the destination address for forwarding
UDP broadcast packets, including BOOTP.
Step 4
exit
Return to global configuration mode.
Step 5
ip forward-protocol {udp [port] | nd | sdns} Specify which protocols the router forwards when forwarding
broadcast packets.
Step 6
end
Return to privileged EXEC mode.
Step 7
show ip interface [interface-id]
show running-config
Verify the configuration on the interface or all interfaces.
Step 8
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Enter interface configuration mode, and specify the interface to
configure.
Step 3
ip broadcast-address ip-address
Enter a broadcast address different from the default, for example
128.1.255.255.
Step 4
end
Return to privileged EXEC mode.
Step 5
show ip interface [interface-id]
Verify the broadcast address on the interface or all interfaces.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.