R21xx-HP FlexFabric 11900 Layer 3 IP Services Configuration Guide

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Configuring UDP helper
Overview
UDP helper enables a device to convert received UDP broadcast packets into unicast packets and
forward them to a specific server. UDP helper is suitable for the scenario where hosts cannot obtain
configuration information or device names by broadcasting packets because the target server or host
resides on another broadcast domain.
Upon receiving a UDP broadcast packet (the destination address is 255.255.255.255 or a directed
broadcast address destined for the network directly connected to the receiving interface), UDP helper
matches the UDP destination port number of the packet against the configured UDP ports.
• If a match is found, UDP helper modifies the destination IP address of the packet and sends the
packet to the specified destination server.
• If no match is found, UDP helper sends the packet to the upper layer protocol.
Configuration guidelines
Follow these guidelines when you configure UDP helper:
• The switches do not receive directed broadcast destined to directly connected networks by default.
To use UDP helper, execute the ip forward-broadcast command in interface view. For more
information about receiving directed broadcasts destined for the directly connected network, see
"Optimizing IP performance."
• UDP helper 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 up to 256 UDP ports for UDP helper.
• Specify destination servers on the interface that receives broadcast packets. You can specify up to
20 destination servers on an interface.
Configuration procedure
Step Command Remarks
1. Enter system view.
system-view N/A
2. Enable UDP helper.
udp-helper enable
By default, UDP helper is
disabled.
3. Specify a UDP port.
udp-helper port { port-number | dns |
netbios-ds | netbios-ns | tacacs | tftp |
time }
By default, no UDP port is
specified.