Chapter 1 UDP-Helper Configuration
1.1 Introduction to UDP-Helper
UDP-Helper is designed to relay specified
UDP broadcast packets. It enables a device to operate as a UDP packet relay.
That is, it can convert UDP broadcast packets into unicast packets and forward
them to a specified server.
Normally, all the received UDP broadcast
packets are passed to the UDP module. With the UDP-Helper function enabled, the
device checks the destination port numbers of the received UDP broadcast
packets and duplicates those with their destination port numbers being that configured
for UDP-Helper to the UDP-Helper module. The UDP-helper module in turn modifies
the destination IP addresses of the packets and then sends the packet to the
specified destination server.
The DHCP Relay
module uses UDP port 67 and 68 to relay BOOTP/DHCP broadcast packets, so do not
use port 67 and 68 as UDP-Helper destination ports.
With UDP-Helper enabled, the device relays
the UDP broadcast packets whose destination ports are one of the six UDP ports
list in Table 1-1 by default.
Table 1-1 List of default UDP ports
|
Protocol
|
UDP port number
|
|
Trivial file transfer protocol (TFTP)
|
69
|
|
Domain name system (DNS)
|
53
|
|
Time service
|
37
|
|
NetBIOS name service (NetBIOS-NS)
|
137
|
|
NetBIOS datagram service (NetBIOS-DS)
|
138
|
|
TACACS (terminal access controller access
control system)
|
49
|
1.2 Configuring UDP-Helper
Table 1-2
|
Operation
|
Command
|
Description
|
|
Enter
system view
|
system-view
|
—
|
|
Enable
UDP-Helper
|
udp-helper enable
|
Required
UDP-Helper
is disabled by default
|
|
Configure
a UDP port as a UDP-Helper destination port
|
udp-helper
port { port-number
| dns | netbios-ds | netbios-ns | tacacs | tftp
| time }
|
This
operation is unnecessary if the port is among the default UDP ports listed in
Table 1-1.
With
UDP-Helper enabled, UDP broadcast packets destined for the ports listed in Table 1-1 are relayed by default.
|
|
Enter
VLAN interface view
|
interface
vlan-interface vlan-id
|
—
|
|
Configure
the destination server to which the matched UDP broadcast packets are to be
forwarded
|
udp-helper
server ip-address
|
Required
By default, no destination server is configured
|
Caution:
l
You need to enable the
UDP-Helper function before specifying a UDP-Helper destination port.
l
The dns, netbios-ds, netbios-ns,
tacacs, tftp, and time keywords refers to the six default
UDP ports. You can configure a default port to be a UDP-Helper destination port
by specifying the corresponding port number or the corresponding keyword. For
example, udp-helper port 53 and udp-helper port dns
specify the same port as a UDP-Helper destination port.
l
The display current-configuration command
does not display the default UDP ports that are configured to be UDP-Helper
destination ports.
l
After UDP-Helper is disabled, all the configured
UDP ports are cancelled, including the default ports.
l
You can configure up to 40 UDP ports as
UDP-Helper destination ports on a device.
l
You can configure up to 20 destination servers
on a VLAN interface.
l
If the destination server is configured on a
VLAN interface, the UDP broadcast packets received from the ports in the VLAN with
specific UDP-Helper destination ports are forwarded to the destination server
configured on the VLAN interface.
After performing the above configurations,
you can use the display command in any view to display the information
about the destination servers and the number of the packets forwarded to each
destination server. Verify the configuration by checking the output
information. You can use the reset command in user view to clear
statistics about packets forwarded by UDP-Helper. You can also use the debugging
command in user view to debug UDP-Helper.
Table 1-3
Display and debug UDP-Helper
|
Operation
|
Command
|
Description
|
|
Display the information about the destination
servers and the number of the packets forwarded to each destination server
|
display udp-helper server [ interface vlan-interface
vlan-id ]
|
You can use the display command in
any view
|
|
Clear the statistics about packets
forwarded by UDP-Helper
|
reset udp-helper packet
|
You can use the reset command in
user view
|
|
Enable debugging for UDP-Helper
|
debugging
udp-helper { event | packet [ receive
| send ] }
|
You can use the debugging command
in user view
|
1.4 UDP-Helper Configuration Example
The IP address of VLAN 1 interface is
10.110.1.1/16. The VLAN interface is connected to the network segment
10.110.0.0/16. Configure to forward the broadcast UDP packets whose destination
UDP port number is 55 to the server with its IP address being 202.38.1.2/24.
Figure
1-1 Network diagram for UDP-Helper configuration
This example
assumes that the port through which the switch is connected to the Internet
belongs to VLAN 1 and the route between the switch and the network segment
202.38.1.0/24 is reachable.
# Enable UDP-Helper.
<H3C> system-view
[H3C] udp-helper enable
# Configure port 55 as a UDP-Helper
destination port.
[H3C] udp-helper port 55
Port has been configured. Please
check the port again.
# Configure the server with the IP address
of 202.38.1.2 as a destination server for the UDP broadcast packets.
[H3C] interface Vlan-interface 1
[H3C-Vlan-interface1] ip address
10.110.1.1 16
[H3C-Vlan-interface1] udp-helper
server 202.38.1.2
