Configuring UDP helper
The term "interface" in this chapter collectively refers to VLAN interfaces and Layer 3 Ethernet interfaces.
You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see
Layer 2
LAN Switching Configuration Guide).
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Overview
UDP helper functions as a relay agent that converts UDP broadcast packets into unicast packets and
forwards them to a specified destination server. This is helpful when a host cannot obtain network
configuration information or request device names through broadcasting because the server or host to be
requested is located on another broadcast domain.
With UDP helper enabled, a device decides whether to forward a received UDP broadcast packet
according to the UDP destination port number of the packet.
If the destination port number of the packet matches the one pre-configured on the device, the
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device modifies the destination IP address in the IP header, and then sends the packet to the
specified destination server.
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If the destination port number of the packet does not match the one pre-configured on the device,
the device sends the packet to the upper layer protocol for processing.
Configuration restrictions and guidelines
The receiving of directed broadcasts to a directly connected network is disabled by default on the
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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 "Configuring IP performance optimization."
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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.
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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.
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You can configure up to 256 UDP port numbers to enable the forwarding of packets with these UDP
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port numbers.
You can configure up to 20 destination servers on an interface.
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Configuration procedure
To configure UDP helper:
Step
1.
Enter system view.
2.
Enable UDP helper.
Command
system-view
udp-helper enable
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Remarks
N/A
Disabled by default.