3Com Switch 7750 Configuration Guide Guide

UDP-HELPER CONFIGURATION

Introduction to

UDP-Helper

UDP-Helper is designed to relay specified UDP broadcast packets. It enables a

device to operate as a UDP packet relay. That is, it can convert UDP broadcast

packets into unicast packets and forward them to a specified server.

Normally, all the received UDP broadcast packets are passed to the UDP module.

With the UDP-Helper function enabled, the device checks the destination port

numbers of the received UDP broadcast packets and duplicates those with their

destination port numbers being that configured for UDP-Helper to the UDP-Helper

module. The UDP-helper module in turn modifies the destination IP addresses of

the packets and then sends the packet to the specified destination server.

The DHCP Relay module uses UDP port 67 and 68 to relay BOOTP/DHCP broadcast

packets, so do not use port 67 and 68 as UDP-Helper destination ports.

With UDP-Helper enabled, the device relays the UDP broadcast packets whose

destination ports are one of the six UDP ports list in

Table 532 by default.

Configuring

UDP-Helper

Table 532 List of default UDP ports

Protocol UDP port number

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

TACACS (terminal access controller access control system) 49

Table 533 Configure UDP-Helper

Operation Command Description

Enter system view system-view -

Enable UDP-Helper udp-helper enable

Required

UDP-Helper is disabled by

default