3com 5500-SI Manual De Usuario

UDP Helper Configuration 303

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This section contains UDP Helper configuration information.

The major function of the UDP Helper is to relay-forward UDP broadcast packets, that 
is, it can convert UDP broadcast packets into unicast packets and send them to the 
designated server, as a relay.

When UDP Helper starts, the Switch can judge whether to forward the UDP broadcast 
packets received at the port based on UDP port ID. If yes, the Switch then modifies 
the IP address in the IP packet header and sends the packet to the designated 
destination server. Otherwise, it sends the packet to the upper layer module for 
further processing. For the BOOTP/DHCP broadcast packet, if the client specifies in 
the request message that the response message needs to be received as broadcast 
packet, then the Switch broadcasts the response message to the client. Otherwise, it 
unicasts the response message.

UDP Helper configuration includes:

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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. 

By default, the UDP Helper function is disabled. 

When the UDP relay function is enabled, by default the system forwards the 
broadcast packets on the UDP ports listed in Table 300. You can configure up to 256 
UDP ports with the relay function. 

Table 299   Enabling/Disabling UDP Helper function

Enable UDP Helper function

Disable UDP Helper function

Table 300   Default UDP Ports List

Trivial File Transfer Protocol (TFTP)

69

Domain Name System (DNS)

53

Time service

37