Command Reference Guide

IP Helper Commands
CLI Command Reference
September 2014 Page 547
HP Moonshot Switch Module CLI Command Reference
The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client to one or
more DHCP servers, and relays to the client packets that the DHCP server unicasts back to the relay agent. For
other protocols, the relay agent only relays broadcast packets from the client to the server. Packets from the
server back to the client are assumed to be unicast directly to the client. Because there is no relay in the return
direction for protocols other than DHCP, the relay agent retains the source IP address from the original client
packet. The relay agent uses a local IP address as the source IP address of relayed DHCP client packets.
When a switch receives a broadcast UDP packet on a routing interface, the relay agent checks if the interface
is configured to relay the destination UDP port. If so, the relay agent unicasts the packet to the configured
server IP addresses. Otherwise, the relay agent checks if there is a global configuration for the destination UDP
port. If so, the relay agent unicasts the packet to the configured server IP addresses. Otherwise the packet is
not relayed. Note that if the packet matches a discard relay entry on the ingress interface, then the packet is
not forwarded, regardless of the global configuration.
The relay agent only relays packets that meet the following conditions:
• The destination MAC address must be the all-ones broadcast address (FF:FF:FF:FF:FF:FF)
• The destination IP address must be the limited broadcast address (255.255.255.255) or a directed
broadcast address for the receive interface.
• The IP time-to-live (TTL) must be greater than 1.
• The protocol field in the IP header must be UDP (17).
• The destination UDP port must match a configured relay entry.
clear ip helper statistics
Use this command to reset to zero the statistics displayed in the show ip helper statistics command.
Example: The following shows an example of the command.
(Routing) #clear ip helper statistics
Format
clear ip helper statistics
Mode Privileged EXEC