H3C Technologies H3C S3600 Series Switches - Manual (Page 850)

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z On an S3600 Series Ethernet Switch, the reception of directed broadcast packets to a directly
connected network is disabled by default. As a result, UDP Helper is available only when the ip
forward-broadcast command is configured in system view. For details about the ip
forward-broadcast command, refer to the IP Address and Performance part of this manual.
z You need to enable UDP Helper before specifying any UDP port to match UDP broadcasts;
otherwise, the configuration fails. When the UDP helper function is disabled, all configured UDP
ports are disabled, including the default ports.
z The dns, netbios-ds, netbios-ns, tacacs, tftp, and time keywords correspond to the six default
ports. You can configure the default ports by specifying port numbers or the corresponding
parameters. For example, udp-helper port 53 and udp-helper port dns specify the same port.
z You can specify up to 20 destination server addresses on a VLAN interface.
z If UDP Helper is enabled after a destination server is configured for a VLAN interface, the
broadcasts from interfaces belonging to the VLAN and having a matching UDP port will be unicast
to the destination server.
Displaying and Maintaining UDP Helper
To do… Use the command… Remarks
Display the UDP broadcast
relay forwarding information of
a specified VLAN interface on
the switch
display udp-helper server
[ interface vlan-interface
vlan-id ]
Available in any view
Clear statistics about packets
forwarded by UDP Helper
reset udp-helper packet Available in user view
UDP Helper Configuration Example
Cross-Network Computer Search Through UDP Helper
Network requirements
PC A resides on network segment 192.168.1.0/24 and PC B on 192.168.10.0/24; they are connected
through Switch A and are routable to each other. It is required to configure UDP Helper on the switch, so
that PC A can find PC B through computer search. (Broadcasts with UDP port 137 are used for
searching.)