R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

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Configuring UDP helper
Overview
UDP helper enables a device to convert received UDP broadcast packets into unicast packets and
forward them to a specific server. UDP helper is suitable for the scenario where hosts cannot obtain
configuration information or device names by broadcasting packets because the target server or host
resides on another broadcast domain.
Upon receiving a UDP broadcast packet, UDP helper matches the UDP destination port number of the
packet against the configured UDP ports.
• If a match is found, UDP helper modifies the destination IP address of the packet, and sends the
packet to the specified destination server.
• If no match is found, UDP helper sends the packet to the upper layer protocol.
Configuring UDP helper
• UDP helper can be configured on VLAN interfaces and Layer 3 Ethernet interfaces (including
subinterfaces) only.
• Some devices do not receive directed broadcast destined to directly connected networks by default.
To use UDP helper on these devices, you must execute the ip forward-broadcast command in system
view. For more information about reception and forwarding of directed broadcasts destined to
directly connected networks, see "Optimizing IP performance."
• 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 a UDP port to forward packets.
For example, udp-helper port 53 and udp-helper port dns specify the same UDP port number.
• All UDP ports configured for UDP helper are removed if you disable UDP helper.
• You can specify up to 256 UDP ports for UDP helper.
• You can specify 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 The default setting is disabled.
3. Specify a UDP port.
udp-helper port { port-number | dns |
netbios-ds | netbios-ns | tacacs | tftp
| time }
No UDP port is specified by
default.