Table of Contents

1 UDP Helper Configuration Guide· 1-1

Configuring UDP Helper 1-1

Network Diagram·· 1-1

Networking and Configuration Requirements· 1-1

Applicable Product Matrix· 1-1

Configuration Procedure· 1-2

Complete Configuration· 1-2

Configuration Guidelines· 1-2

Configuring 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 Ethernet switch provides the UDP Helper function to relay specified UDP broadcast 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 its UDP destination port number.

l          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.

l          If not, the device sends the packet to the upper layer protocol for processing.

Network Diagram

Figure 1-1 Network diagram for UDP Helper configuration

Networking and Configuration Requirements

l          VLAN-interface 1 on Switch A has an IP address of 10.110.1.1/16 and is connected to network segment 10.110.0.0/16.

l          Enable the forwarding of broadcast packets with UDP destination port number 55 to the destination server 10.2.1.1/16.

Applicable Product Matrix

Configuration Procedure

The following configuration assumes that a route from Switch A to the network segment 10.2.0.0/16 is available.

# Enable UDP Helper on Switch A.

<SwitchA> system-view

[SwitchA] udp-helper enable

# Enable the forwarding of broadcast packets with the UDP destination port number 55.

[SwitchA] udp-helper port 55

# Specify the server with the IP address of 10.2.1.1 as the destination server to which UDP packets are to be forwarded.

[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

Complete Configuration

#

 udp-helper enable

 udp-helper port 55

#

interface Vlan-interface1

 ip address 10.110.1.1 255.255.0.0

 udp-helper server 10.2.1.1

#

Configuration Guidelines

l          The UDP Helper enabled device cannot forward DHCP broadcast packets. That is, the UDP port number cannot be set to 67 or 68.

l          By default, the receiving of directed broadcasts to a directly connected network is disabled on S3610 and S5510 series Ethernet switches. As a result, UDP Helper is available only when the ip forward-broadcast command is configured in system view. If DHCP or NTP broadcast mode is configured on an S3610 or S5510 switch, the switch can receive directed broadcasts. At this time, UDP Helper is available even if the ip forward-broadcast command is not configured. For details about the ip forward-broadcast command, refer to IP Addressing and IP Performance Commands of the related product manual.

l          Before specifying UDP port numbers with which packets are to be forwarded, you need to enable UDP Helper; otherwise, an error message is displayed. Disabling UDP Helper also disables the specified UDP port numbers.