Enabling UDP Application Forwarding

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.

In the following table, the UDP applications (from RFC 1340) are listed with the port number in parentheses. If you specify an application name, use the name only. You can also specify any UDP application by entering just the UDP port number as listed:

  • 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)

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

  1. Enter global configuration mode. 
    device# configure terminal
  2. Enable the forwarding of NTP broadcasts. 
    device(config)# ip forward-protocol udp ntp
Parent topic: UDP broadcast and IP helper