3Com SuperStack 4 Configuration Manual page 93

Note:
After you have configured DHCP Relay, the Switch automatically configure
■
UDP-Helper whether the Switch is a single unit or in a fabric. The UDP-Helper
configuration remains when you remove the DHCP Relay configuration.
If you remove UDP-Helper configuration when the DHCP Relay configuration
■
still remains, the Switch will display the following prompt
DHCP Relay errors
the UDP-Helper configuration.
Enabling/Disabling UDP Helper Function
When the 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, the relay function configured at
all UDP ports, including the default six ports, is disabled.
Perform the following configuration in System View.
Table 100 Enabling/Disabling UDP Helper function
Operation
Enable UDP Helper function
Disable UDP Helper function
By default, the UDP Helper function is disabled.
Configuring UDP Port with Replay Function
When the UDP relay function is enabled, by default the system forwards the
broadcast packets on the UDP ports listed in
256 UDP ports with the relay function.
Table 101 Default UDP Ports List
Protocol
Trivial File Transfer Protocol (TFTP)
Domain Name System (DNS)
Time service
NetBIOS Name Service (NetBIOS-NS)
NetBIOS Datagram Service (NetBIOS-DS)
Terminal Access Controller Access Control System (TACACS)
Perform the following configuration in System View.
Table 102 Configuring UDP Port with Replay Function
Operation
Configure UDP port with
replay function
Remove the configuration
, and you will need to confirm if you really want to remove
Command
udp-helper enable
undo udp-helper enable
Table
Command
udp-helper port {
netbios-ns | tacacs | tftp | time}
undo udp-helper port {
netbios-ns | tacacs | tftp | time }
UDP Helper Configuration
This may result in
101. You can configure up to
UDP port ID
69
53
37
137
138
49
| dns | netbios-ds |
port
| dns | netbios-ds |
port
105