Chapter 1 UDP Helper Configuration
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
l
UDP Helper Configuration
Example
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By default, S5500-SI series Ethernet switches do
not forward IP broadcast packets. So, to utilize the UDP Helper function, you need
to execute the ip forward-broadcast command in system view first. For
details, refer to the IP Address and Performance part of the manual.
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Currently, interface-related configurations concerning
the UDP Helper function can only be performed on VLAN interfaces.
1.1 Introduction to UDP Helper
UDP Helper makes the device to function as
a relay that converts UDP broadcast packets into unicast packets and forwards
them to a specified server.
With UDP Helper enabled, the device decides
whether to forward a received UDP broadcast packet according to the UDP port
number of the packet. If the packet needs to be forwarded, the device modifies
the destination IP address in the IP header and then sends the packet to the
specified destination server. Otherwise, the device passes the packet to the
upper layer for the packet to be processed.
With UDP Helper
enabled, the device relays broadcast packets of six default UDP ports by
default. The default UDP ports are listed in Table 1-1.
Table 1-1 List
of default UDP ports
|
Protocol
|
UDP port number
|
|
TFTP (trivial file transfer protocol)
|
69
|
|
DNS (domain name system)
|
53
|
|
Time service
|
37
|
|
NetBIOS-NS (NetBIOS name service)
|
137
|
|
NetBIOS-DS (NetBIOS datagram service)
|
138
|
|
TACACS (terminal access controller access
control system)
|
49
|
1.2 Configuring UDP Helper
Table 1-2 Follow these steps to
configure UDP Helper
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
—
|
|
Enable UDP Helper
|
udp-helper enable
|
Required
Disabled by default
|
|
Specify a UDP port
|
udp-helper port { port-number | dns | netbios-ds | netbios-ns
| tacacs | tftp | time }
|
Optional
By default, the UDP helper enabled device
converts and forwards broadcast packets of ports 69, 53, 37, 137, 138, and
49.
|
|
Enter VLAN interface view
|
interface interface-type interface-number
|
—
|
|
Configure the destination server to which
the UDP broadcast packets are to be forwarded
|
udp-helper server ip-address
|
Required
No destination server is configured by
default.
|
Caution:
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The dns, netbios-ds, netbios-ns,
tacacs, tftp, and time keywords correspond to the six default
ports. You can configure the default ports by specifying port numbers or the
corresponding parameters. For example, udp-helper port 53 and udp-helper
port dns specify the same port.
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When you view the configuration information by
using the display current-configuration command, the UDP Helper
configuration on default UDP ports is not displayed. The UDP Helper
configuration of a default UDP port is displayed only when UDP Helper is
disabled on the port.
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The configuration of all UDP ports (including
the default ports) is removed if you disabled UDP Helper.
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You can configure up to 256 UDP ports that
require relaying and forwarding.
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You can configure up to 20 destination servers
at an interface.
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If the destination server is configured on a
VLAN interface, the broadcast packets from a VLAN port to a specific UDP port
will be unicast to the destination server configured on that VLAN interface after
UDP Helper is enabled.
1.3 Displaying and Maintaining UDP Helper
Table 1-3 Displaying and maintaining UDP
Helper
|
To do…
|
Use the command…
|
Remarks
|
|
Display the information of the
destination server and the number of packets forwarded by UDP relay
|
display udp-helper server [ interface interface-type interface-number ]
|
Available in any view
|
|
Clear statistics about packets forwarded
by UDP relay
|
reset udp-helper packet
|
Available in user view
|
1.4 UDP Helper Configuration Example
I. Network requirements
The VLAN interface of a device has an IP
address of 10.110.1.1/16, connecting to network segment 10.110.0.0/16. Specify
to forward broadcast packets with destination UDP port 55 to destination server
202.38.1.2/24.
II. Network diagram
Figure 1-1 Network diagram for UDP
Helper configuration
III. Configuration procedure
The following
configuration assumes that the route between the device and the network segment
202.38.0.0/24 is reachable.
# Enable UDP Helper.
<Sysname> system-view
[Sysname] udp-helper enable
# Specify to forward the broadcast packets
with destination UDP port being 55.
[Sysname] udp-helper port 55
# Specify the server with the IP address of
202.38.1.2 as the destination server to which UDP broadcast packets are to be
forwarded.
[Sysname] interface Vlan-interface 1
[Sysname-Vlan-interface1] ip address
10.110.1.1 16
[Sysname-Vlan-interface1] udp-helper
server 202.38.1.2
