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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 35 Configuring IP Unicast Routing
Configuring IP Addressing
By default, both UDP and ND forwarding are enabled if a helper address has been defined for an
interface. The description for the ip forward-protocol interface configuration command in the Cisco
IOS IP Command Reference, Volume 1 of 3: Addressing and Services, Release 12.2 lists the ports that
are forwarded by default if you do not specify any UDP ports.
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 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:
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
no shutdown Enable the interface if necessary. By default, UNIs and ENIs are
disabled and NNIs are enabled.
Step 4
ip helper-address address Enable forwarding and specify the destination address for forwarding
UDP broadcast packets, including BOOTP.
Step 5
exit Return to global configuration mode.
Step 6
ip forward-protocol {udp [port] | nd | sdns} Specify which protocols the router forwards when forwarding
broadcast packets.
Step 7
end Return to privileged EXEC mode.
Step 8
show ip interface [interface-id]
or
show running-config
Verify the configuration on the interface or all interfaces.
Step 9
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
no shutdown Enable the interface if necessary. By default, UNIs and ENIs are
disabled and NNIs are enabled.