Enabling forwarding for a UDP application

If you want the Layer 3 switch to forward client requests for UDP applications that the Layer 3 switch does not forward by default, you can enable forwarding support for the port. To enable forwarding support for a UDP application, use the following method. You also can disable forwarding for an application using this method.

NOTE

You also must configure a helper address on the interface that is connected to the clients for the application. The Layer 3 switch cannot forward the requests unless you configure the helper address.

To enable the forwarding of NTP broadcasts, enter the following command.

device(config)# ip forward-protocol udp ntp

Syntax: [no] ip forward-protocol {udp udp-port-name | udp-port-num }

The udp-port-name parameter can have one of the following values. For reference, the corresponding port numbers from RFC 1340 are shown in parentheses. If you specify an application name, enter the name only, not the parentheses or the port number shown here:

bootpc (port 68)
bootps (port 67)
discard (port 9)
dns (port 53)
dnsix (port 90)
echo (port 7)
mobile-ip (port 434)
netbios-dgm (port 138)
netbios-ns (port 137)
ntp (port 123)
tacacs (port 65)
talk (port 517)
time (port 37)
tftp (port 69)

In addition, you can specify any UDP application by using the application UDP port number.

The udp-port-num parameter specifies the UDP application port number. If the application you want to enable is not listed above, enter the application port number. You also can list the port number for any of the applications listed above.

To disable forwarding for an application, enter a command such as the following.

device(config)# no ip forward-protocol udp ntp

This command disables forwarding of SNMP requests to the helper addresses configured on Layer 3 switch interfaces.

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Enabling forwarding for a UDP application