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06-UDP Helper Configuration | 32.69 KB |
When configuring UDP Helper, go to these sections for information you are interested in:
l Overview
UDP Helper (UDPH) functions as a relay agent that converts UDP broadcast packets into unicast packets and forwards them to a specified server.
With the UDP Helper function enabled, the device decides whether to forward a received UDP broadcast packet according to the UDP port number of the packet. If the packet needs to be forwarded, the device modifies the destination IP address in the IP header and then sends the packet to the specified destination server. Otherwise, the device sends the packet to its upper layer module.
The router to be configured is reachable.
Follow these steps to configure UDP Helper:
To do… |
Use the command… |
Remarks |
Enter system view |
system-view |
— |
Enable the function of forwarding UDP broadcast packets |
udp-helper enable |
Required By default, the function is disabled. l When the function is enabled, the function is enabled on the six default ports (69, 53, 37, 137, 138, and 49) simultaneously. l When the function is disabled, the function is disabled on all the ports, including the default ports. |
Specify UDP ports that the packets to be forwarded contain |
udp-helper port { port | dns | netbios-ds | netbios-ns | tacacs | tftp | time } |
Optional l When the function is enabled, the broadcast packets with the default UDP ports are unicast to the corresponding destination server. Refer to Table 1-1 for the list of default UDP ports. l The system supports up to 256 UDP ports. l The UDP port number is in the range of 1 to 65,535. UDP broadcast packets of port 0, port 67, and port 68 cannot be forwarded. |
Enter VLAN interface view |
interface vlan-interface interface -number |
— |
Configure the destination server to which the UDP packets are forwarded |
udp-helper server ip-address |
Required l Up to 20 destination servers are corresponding to a VLAN interface. l Suppose a destination server is configured on a VLAN interface. When the function of forwarding UDP broadcast packets is enabled, all the broadcast packets received on the VLAN interface from the specified UDP ports are unicast to the destination server corresponding to the VLAN interface. l By default, the destination server to which the UDP packets are forwarded is not configured. |
Table 1-1 shows the list of default UDP ports.
Table 1-1 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 server (NetBIOS-NS) |
137 |
NetBIOS datagram server (NetBIOS-DS) |
138 |
Terminal access controller access control system (TACACS) |
49 |
Note that:
1) You cannot specify the UDP ports before the function of forwarding UDP broadcast packets is enabled. Otherwise, the system displays error information.
2) The dns | netbios-ds | netbios-ns | tacacs | tftp | time keyword refers to six default UDP ports. You can specify a default UDP port in one of the two following ways:
l Specifying the port number.
l Specifying the keyword.
For example, the udp-helper port 53 command specifies the same port as the udp-helper port dns command.
3) The display current-configuration command does not display the default port numbers. A default port number is displayed when the function of forwarding UDP broadcast packets is disabled on this port.
4) You can use the udp-helper server command to configure the IP address of the destination server as the address of a host or the broadcast address of a subnet, but not as a limited broadcast address.
5) If the undo udp-helper server command is executed without any parameters, all destination servers configured on the VLAN interface are removed.
To do… |
Use the command… |
Remarks |
Display the information of the destination servers corresponding to the VLAN interface |
display udp-helper { server [ interface vlan-interface vlan-id ] | port } |
Available in any view |