3Com Switch 8800 Advanced Software V5 Configuration Guide

714 CHAPTER 48: UDP HELPER CONFIGURATION
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CAUTION:
■ 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.
■ The dns, netbios-ds, netbios-ns, tacacs, tftp, and time keywords
correspond to the six default UDP port numbers. You can configure these
default UDP port numbers by specifying port numbers or the corresponding
parameters. For example, udp-helper port 53 and udp-helper port dns
specify the same UDP port number.
■ When you view the configuration information by using the display
current-configuration command, the UDP Helper configuration of the
default ports will not be displayed. UDP Helper configuration of these ports will
be displayed only after UDP Helper is disabled.
■ The configuration of all UDP ports (including the default ports) is removed if
you disable UDP Helper.
■ You can configure up to 256 UDP port numbers to enable the forwarding of
packets with these UDP port numbers.
■ You can configure up to 20 destination servers on an interface.
■ If a destination server is configured on a VLAN interface, broadcast packets
with the specified UDP destination port number that are received from a VLAN
port will be unicast to that destination server after UDP Helper is enabled.
Displaying and
Maintaining UDP
Helper
Enable UDP Helper udp-helper enable Required
Disabled by default
Enable the forwarding of
packets with the specified
UDP destination port
number(s)
udp-helper port {
port-number | dns |
netbios-ds | netbios-ns |
tacacs | tftp | time }
Optional
By default, the UDP helper
enabled device forwards
broadcast packets with
destination port numbers 69,
53, 37, 137, 138, and 49.
Enter VLAN interface view interface interface-type
interface-number
-
Configure the destination
server to which UDP packets
are to be forwarded
udp-helper server ip-address Required
By default, no destination
server is configured.
To do... Use the command... Remarks
To do... Use the command... Remarks
Display the information of the
destination servers and the
number of packets forwarded
to the destination servers
display udp-helper server [
interface interface-type
interface-number ]
Available in any view
Clear statistics about packets
forwarded
reset udp-helper packet Available in user view