H3C Technologies H3C S10500 Series Switches - Manual (Page 109)

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CAUTION:
•
The receiving of directed broadcasts to a directly connected network is disabled by default on the switch.
As a result, UDP Helper is available only when the ip forward-broadcast command is configured in
system view. For more information about reception and forwarding of directed broadcasts to a directly
connected network, see the chapter “IP performance optimization
configuration.”
• A UDP Helper enabled device must not forward DHCP broadcast packets that use destination port 67 or
68. Therefore, the UDP port numbers set with the udp-helper port command must not include 67 or 68.
• You can specify a port number or the corresponding parameter for a UDP port to forward packets. For
example, udp-helper port 53 and udp-helper port dns specify the same UDP port number.
• The configuration of all UDP ports is removed if you disable UDP Helper.
• You can configure up to 256 UDP port numbers to enable the forwarding of packets with these UDP port
numbers.
• You can configure up to 20 destination servers on an interface.
Displaying and maintaining UDP Helper
To do… Use the command… Remarks
Displays the information of
forwarded UDP packets
display udp-helper server [ interface
interface-type interface-number ] [ | { begin
| exclude | include } regular-expression ]
Available in any view
Clear statistics about packets
forwarded
reset udp-helper packet Available in user view
UDP Helper configuration example
Network requirements
As shown in Figure 43 , the IP address of VLAN-interface 1 of Switch A is 10.110.1.1/16, and the interface
connects to the subnet 10.110.0.0/16.
Configure UDP Helper to forward broadcast packets with UDP destination port number 55 and
destination IP address 255.255.255.255 or 10.110.255.255 to the destination server 10.2.1.1/16.
Figure 43 Network diagram for UDP Helper configuration
Configuration procedure
NOTE:
Check that a route from Switch A to the subnet 10.2.0.0/16 is available.