Operation Manual – UDP Helper
H3C S3610&S5510 Series Ethernet Switches
Chapter 1 UDP Helper Configuration
1-1
Chapter 1 UDP Helper Configuration
When configuring UDP Helper, go to these sections for information you are interested
in:
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Displaying and Maintaining UDP Helper
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UDP Helper Configuration Example
1.1 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.
By default, with UDP Helper enabled, the device forwards broadcast packets with the
six UDP destination port numbers listed in
.
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 service (NetBIOS-NS)
137
NetBIOS datagram service (NetBIOS-DS)
138
Terminal access controller access control system (TACACS)
49
