When configuring UDP Helper, go to these
sections for information you are interested in:
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Introduction
to UDP Helper
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Configuring
UDP Helper
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Displaying
and Maintaining UDP Helper
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UDP
Helper Configuration Example
1.1 Introduction to 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 device provides
the UDP Helper function to relay specified UDP 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 the UDP
destination port number of the packet.
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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.
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If not, the device sends the packet to the upper
layer protocol for processing.
1.2 Configuring UDP Helper
Follow these steps to configure UDP Helper:
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To do…
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Use the command…
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Remarks
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Enter system view
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system-view
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—
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Enable UDP Helper
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udp-helper enable
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Required
Disabled by default.
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Enable the forwarding of packets with the
specified UDP destination port number(s)
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udp-helper port { port-number | dns | netbios-ds | netbios-ns
| tacacs | tftp | time }
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Required
By default, no UDP port number is
specified.
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Enter VLAN interface view
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interface Vlan-interface vlan-id
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—
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Specify the destination server to which
UDP packets are to be forwarded
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udp-helper server ip-address
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Required
No destination server is specified by
default.
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Caution:
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The UDP Helper enabled device cannot forward
DHCP broadcast packets. That is to say, the UDP port number cannot be set to 67
or 68.
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For the dns, netbios-ds, netbios-ns, tacacs,
tftp, and time keywords, you can specify
port numbers or the corresponding parameters. For example, udp-helper port
53 and udp-helper port dns specify the same UDP port number.
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The configuration of all UDP ports is removed if
you disable UDP Helper.
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You can configure up to 20 destination servers
on a VLAN interface.
1.3 Displaying and Maintaining UDP Helper
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To do…
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Use the command…
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Remarks
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Displays the information of forwarded UDP
packets
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display udp-helper server [ interface Vlan-interface vlan-id ]
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Available in any view
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Clear statistics about packets forwarded
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reset udp-helper packet
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Available in user view
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I. Network requirements
The interface VLAN-interface 1 of Switch A
has the IP address of 10.110.1.1/16, connecting to the network segment
10.110.0.0/16. Enable the forwarding of broadcast packets with the UDP
destination port number 55 to the destination server 10.2.1.1/16.
II. Network diagram
Figure
1-1 Network diagram for UDP Helper configuration
III. 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.
<SwitchA> system-view
[SwitchA] udp-helper enable
# Enable the forwarding 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
