Allied Telesis x900-48 series - Manual (Page 26)

Page 26 | AlliedWare™ OS How To Note: DHCP snooping on AT-9900-style switches
Troubleshooting > Switch is dropping ARPs
Switch is dropping ARPs
If you have DHCP snooping in ARP security mode, then unknown clients on untrusted ports
will not be able to ARP.
Known clients on untrusted ports will be able to ARP.
A client is known on an untrusted port if it has an IP/MAC entry in the DHCP snooping
database (show dhcpsnooping database). Your DHCP server must be on a trusted port.
You cannot work around dropped ARPs (from the DHCP server) by statically binding the
DHCP server’s IP and MAC address to a port, instead of setting it as trusted. The switch will
not send the DHCP server the DHCP request. The switch will not flood the DHCP request
to any ports other than trusted ones. So although the switch will let the DHCP server send
ARP requests, the DHCP server will not receive any DHCP requests.
DHCPSN_ARP: [0193a9ec] ARP Received on untrusted port 24 VLAN 1
DHCPSN_ARP: [0193a9ec] ARP Discarded, sender not found in DHCP Snoop DB
DHCPSN_ARP: [01a6f5ec] ARP Received on untrusted port 1 VLAN 1
DHCPSN_ARP: [01a6f5ec] ARP to be forwarded, sender validated
DHCPSN_ARP: [01a6f5ec] Forwarding ARP at L2 for VLAN 1
DHCPSN_ARP: [01a6f5ec] Forward ports (except 1)
DHCPSN_ARP: [01a6f5ec] Tagged:None
DHCPSN_ARP: [01a6f5ec] Untagged:24
Manager > set dhcpsnooping port=24 trusted=yes
Info (1137260): DHCP Snooping port(s) 24 updated successfully.
Manager >
DHCPSN_ARP: [023a218c] ARP Received on trusted port 24 VLAN 1
DHCPSN_ARP: [023a218c] Forwarding ARP at L2 for VLAN 1
DHCPSN_ARP: [023a218c] Forward ports (except 24)
DHCPSN_ARP: [023a218c] Tagged:None
DHCPSN_ARP: [023a218c] Untagged:1