Reference Guide

IPv4 Routing | 465
ARP Learning via Gratuitous ARP
Gratuitous ARP can mean an ARP request or reply. In the context of ARP Learning via Gratuitous ARP on
FTOS, the gratuitous ARP is a request. A Gratuitous ARP Request is an ARP request that is not needed
according to the ARP specification, but one that hosts may send to:
• detect IP address conflicts
• inform switches of their presence on a port so that packets can be forwarded
• update the ARP table of other nodes on the network in case of an address change
In the request, the host uses its own IP address in the Sender Protocol Address and Target Protocol Address
fields.
When a Gratuitous ARP is received, FTOS installs an ARP entry on all 3 CPUs.
ARP Learning via ARP Request
When ARP Learning via Gratuitous ARP is enabled, the system installs a new ARP entry, or updates an
existing entry for all received ARP requests.
Command Syntax Command Mode Purpose
clear arp-cache [interface | ip
ip-address] [
no-refresh]
EXEC privilege Clear the ARP caches for all interfaces or for a specific
interface by entering the following information:
• For a port channel interface, enter the keyword
port-channel followed by a number from 1 to 255.
• For a 10-Gigabit Ethernet interface, enter the keyword
TenGigabitEthernet followed by the slot/port
information.
• For a VLAN interface, enter the keyword
vlan followed
by a number between 1 and 4094.
• For a 40-Gigabit Ethernet interface, enter the keyword
fortyGigE followed by the slot/port information.
ip ip-address (OPTIONAL) Enter the keyword ip followed by the
IP address of the ARP entry you wish to clear.
no-refresh (OPTIONAL) Enter the keyword no-refresh to
delete the ARP entry from CAM. Or use this option with interface
or
ip ip-address to specify which dynamic ARP entries you want
to delete.
Note: Transit traffic may not be forwarded during the period
when deleted ARP entries are resolved again and re-installed
in CAM. Use this option with extreme caution.
Task Command Syntax Command Mode
Enable ARP learning via gratuitous ARP.
arp learn-enable
CONFIGURATION