Configuring udp helper, Overview, Configuration restrictions and guidelines – H3C Technologies H3C S12500 Series Switches User Manual
Page 143: Configuration procedure
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Configuring UDP helper
UDP helper can be configured only on VLAN interfaces and Layer 3 Ethernet interfaces (including
subinterfaces).
Overview
UDP helper functions as a relay agent that converts UDP broadcast packets into unicast packets and
forwards them to the specified destination server. This is helpful when a host cannot obtain network
configuration information or request device names through broadcasting because the server or host to be
requested is located on another broadcast domain.
With UDP helper enabled, the switch decides whether to forward a received UDP broadcast packet
according to the UDP destination port number of the packet.
•
If the destination port number of the packet matches the one pre-configured on the switch, the switch
modifies the destination IP address in the IP header, and then sends the packet to the specified
destination server.
•
If not, the switch sends the packet to the upper layer protocol for processing.
Configuration restrictions and guidelines
When you configure UDP helper, follow these restrictions and guidelines:
•
The UDP helper enabled switch cannot forward DHCP broadcast packets. The UDP port number
cannot be set to 67 or 68.
•
You can specify a port number or the corresponding parameter for an UDP port to forward packets.
For example, udp-helper port 53 and udp-helper port dns specify the same UDP port number.
•
The configuration of all UDP 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.
Configuration procedure
To configure UDP helper:
Step Command Remarks
1.
Enter system view.
system-view
N/A
2.
Enable UDP helper.
udp-helper enable
Disabled by default.
3.
Enable the forwarding of
packets with the specified UDP
destination port numbers.
udp-helper port { port-number | dns |
netbios-ds | netbios-ns | tacacs | tftp |
time }
No UDP port number is
specified by default.