9.1 UDP Helper Overview
This section describes the principle of UDP helper.
A host on an intranet needs to obtain the configuration from a server by sending broadcast packets
such as UDP broadcast packets. If the host and the server are located in different broadcast
domains, broadcast packets cannot reach the server and the host cannot obtain the configuration
from the server.
The AR150/200 provides the UDP Helper function to solve this problem. It can relay broadcast
packets with specified UDP ports by converting broadcast packets into unicast packets and
sending the unicast packets to the specified destination server.
9.2 UDP Helper Features Supported by the AR150/200
This section describes the UDP helper features supported by the AR150/200.
After UDP helper is enabled on the AR150/200, the AR150/200 relays broadcast packets with
the default UDP ports to corresponding destination servers. Table 9-1 lists the default UDP
ports. Other UDP ports must be configured manually after UDP helper is enabled.
Table 9-1 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
Terminal Access
Controller Access
Control System
(TACACS)
49
The UDP helper function cannot relay Dynamic Host Configuration Protocol (DHCP) messages,
so the destination port numbers cannot be set to 67 or 68. To relay DHCP messages, enable the
DHCP relay function.
Huawei AR150&200 Series Enterprise Routers
Configuration Guide - IP Service 9 UDP Helper Configuration
Issue 02 (2012-03-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
203
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