H3C Technologies H3C SecPath F1000-E - Manual (Page 300)

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Configuring UDP helper
Overview
UDP helper functions as a relay agent that converts UDP broadcast packets into unicast packets and
forwards them to a 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, a device 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 device, the
device modifies the destination IP address in the IP header, and then sends the packet to the
specified destination server.
• If not, the device sends the packet to the upper layer protocol for processing.
Configuring UDP helper
Configuration guidelines
• On the devices supporting the directed broadcast suppression function, the receiving of directed
broadcasts to a directly connected network is disabled by default. As a result, UDP helper is
available only when the ip forward-broadcast command is configured in system view.
• Do not set UDP ports 67 and 68 for UDP helper, because UDP helper cannot forward DHCP
broadcast packets.
• 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
Step Command Remarks
1. Enter system view system-view N/A
2. Enable UDP helper. udp-helper enable
Required.
Disabled by default.
3. Specify a UDP port.
udp-helper port { port-number | dns |
netbios-ds | netbios-ns | tacacs | tftp
| time }
Required.
No UDP port number is specified
by default.