Configuring UDP helper 1

Overview·· 1

Configuration guidelines 1

Configuration procedure· 1

Displaying and maintaining UDP helper 2

UDP helper configuration example· 2

Network requirements 2

Configuration procedure· 2

Verifying the configuration· 3

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 switch does not receive directed broadcasts destined for the directly connected network by default. To use UDP helper on the switch, execute the ip forward-broadcast command in interface view. For more information about receiving directed broadcasts destined for the directly connected network, see "Configuring IP performance optimization."

·           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 

Displaying and maintaining UDP helper        

Execute display command in any view and reset command in user view.

UDP helper configuration example

By default, Ethernet, VLAN, and aggregate interfaces are down. To configure such an interface, bring the interface up by executing the undo shutdown command.

Network requirements

As shown in Figure 1, 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 1 Network diagram

Configuration procedure

Make sure Switch A can reach the subnet 10.2.0.0/16.

# Enable UDP helper.

[SwitchA] System-view

[SwitchA] udp-helper enable

# Enable UDP helper to forward broadcast packets with the UDP destination port 55.

[SwitchA] udp-helper port 55

# Specify the destination server 10.2.1.1 on VLAN-interface 1.

[SwitchA] interface vlan-interface 1

[SwitchA-Vlan-interface1] ip address 10.110.1.1 16

[SwitchA-Vlan-interface1] udp-helper server 10.2.1.1

# Enable the interface to receive directed broadcasts destined for the directly connected network.

[SwitchA-Vlan-interface1] ip forward-broadcast

Verifying the configuration

# Display information about packets forwarded by UDP helper on VLAN-interface 1.

[SwitchA-Vlan-interface1] display udp-helper interface vlan-interface 1

Interface         Server address       Packets sent

Vlan-interface1   10.2.1.1             5