H3C S5500-SI Series User manual

Operation Manual – UDP Helper
H3C S5500-SI Series Ethernet Switches Table of Contents
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Table of Contents
Chapter 1 UDP Helper Configuration ..........................................................................................1-1
1.1 Introduction to UDP Helper................................................................................................1-1
1.2 Configuring UDP Helper....................................................................................................1-2
1.3 Displaying and Maintaining UDP Helper ...........................................................................1-3
1.4 UDP Helper Configuration Example..................................................................................1-3

Operation Manual – UDP Helper
H3C S5500-SI Series Ethernet Switches Chapter 1 UDP Helper Configuration
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Chapter 1 UDP Helper Configuration
When configuring UDP Helper, go to these sections for information you are interested
in:
zIntroduction to UDP Helper
zConfiguring UDP Helper
zDisplaying and Maintaining UDP Helper
zUDP Helper Configuration Example
Note:
zBy 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.
zCurrently, 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 UDPports
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

Operation Manual – UDP Helper
H3C S5500-SI Series Ethernet Switches Chapter 1 UDP Helper Configuration
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Protocol UDP port number
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.

Operation Manual – UDP Helper
H3C S5500-SI Series Ethernet Switches Chapter 1 UDP Helper Configuration
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Caution:
zThe 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.
zWhen 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.
zThe configuration of all UDP ports (including the default ports) is removed if you
disabled UDP Helper.
zYou can configure up to 256 UDP ports that require relaying and forwarding.
zYou can configure up to 20 destination servers at an interface.
zIf 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.

Operation Manual – UDP Helper
H3C S5500-SI Series Ethernet Switches Chapter 1 UDP Helper Configuration
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II. Network diagram
Ethernet
Internet
Switch ( UDP Helper )
10.110.0.0/16
Ethernet
Server
202.38.1.2/24
10.110.1.1/16
Vlan-interface1
202.38.1.0/24
Ethernet
Internet
Switch ( UDP Helper )
10.110.0.0/16
Ethernet
Server
202.38.1.2/24
10.110.1.1/16
Vlan-interface1
202.38.1.0/24
Figure 1-1 Network diagram for UDP Helper configuration
III. Configuration procedure
Note:
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 IPaddress 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