UDP Helper Configuration With 3Com Switch

The major function of UDP Helper is to relay-forward UDP broadcast packets, that is, it can convert UDP broadcast packets into unicast packets and send to the designated server, as a relay. When UDP Helper starts, the switch can judge if to forward the UDP broadcast packets received at the port based on UDP port ID. If yes, the switch then modifies the IP address in the IP packet header and sends the packet to the designated destination server. Otherwise, it sends the packet to the upper layer module for further processing.

When UDP Helper function is enabled, you can configure the UDP ports where UDP function is required and the relay function is enabled at UDP ports 69, 53, 37, 137, 138 and 49. When the function is disabled. Relay function configured at all UDP ports, including the default six ports, shall be disabled.

Perform the following configuration in system view.

udp-helper enable

When UDP relay function is enabled, the system by default forwards the broadcast packets on the UDP ports . You can configure up to 256 UDP ports with relay function.

Protocol UDP                                                                                                                             port ID
Trivial File Transfer Protocol (TFTP)                                                                         69
Domain Name System (DNS)                                                                                           53
Time service                                                                                                                                  37
NetBIOS Name Service (NetBIOS-NS)                                                                        137
NetBIOS Datagram Service (NetBIOS-DS)                                                              138
Terminal Access Controller Access Control System (TACACS)                49

You can configure up to 20 replay destination servers for a VLAN interface. If a VLAN interface is configured with relay destination servers and UDP Helper function is enabled at it, then the broadcast packets of a designated UDP port received at the VLAN interface will be unicasted to the destination server.

Configure relay destination server for broadcast packet

udp-helper server ip-address

UDP Helper Configuration Example

The IP address of VLAN interface 2 on the switch is, which is connected with network segment Set to relay-forward the broadcast packets with destination IP of all 1s and destination UDP port 55 in the network segment to the destination server


Configuration procedure

1 Enable UDP Helper function.

[4200G] udp-helper enable

2 Set to relay-forward the broadcast packets with destination UDP port 55.

[4200G] udp-helper port 55

3 Set the IP address of the destination server corresponding to VLAN interface 2 as

[4200G] interface vlan 2
[4200G-Vlan-interface2] udp-helper server