3Com 4210G Series, Configuration Manual, Page: 287 / 1133

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UDP Helper Configuration
When configuring UDP Helper, go to these sections for information you are interested in:
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Introduction to UDP Helper
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Configuring UDP Helper
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Displaying and Maintaining UDP Helper
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UDP Helper Configuration Examples
UDP Helper can be currently configured on VLAN interfaces only.
Introduction to UDP Helper
Sometimes, a host needs to forward broadcasts to obtain network configuration information or request
the names of other devices on the network. However, if the server or the device to be requested is
located in another broadcast domain, the host cannot obtain such information through broadcast.
To solve this problem, the device provides the UDP Helper function to relay specified UDP packets. In
other words, UDP Helper functions as a relay agent that converts UDP broadcast packets into unicast
packets and forwards them to a specified destination server.
With UDP Helper enabled, the device decides whether to forward a received UDP broadcast packet
according to the UDP destination port number of the packet.
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If the destination port number of the packet matches the one pre-configured on the device, the
device modifies the destination IP address in the IP header, and then sends the packet to the
specified destination server.
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If not, the device sends the packet to the upper layer protocol for processing.
Configuring UDP Helper
Follow these steps to configure UDP Helper:
To do… Use the command… Remarks
Enter system view
system-view
—
Enable UDP Helper
udp-helper enable
Required
Disabled by default.
Enable the forwarding of
packets with the specified
UDP destination port
number(s)
udp-helper port
{
port-number
|
dns
|
netbios-ds
|
netbios-ns
|
tacacs
|
tftp
|
time
}
Required
No UDP port number is specified
by default.