–ip ip-address (OPTIONAL): enter the keyword ip then the IP address of the ARP entry you
wish to clear.
–no-refresh (OPTIONAL): enter the keywords no-refresh to delete the ARP entry from CAM. Or
to specify which dynamic ARP entries you want to delete, use this option with interface or ip
ip-address.
– For a port channel interface, enter the keywords port-channel then a number.
– For a 10-Gigabit Ethernet interface, enter the keyword TenGigabitEthernet then the slot/port
information.
– For a 40-Gigabit Ethernet interface, enter the keyword fortyGigE then the slot/port information.
– For a VLAN interface, enter the keyword vlan then a number between 1 and 4094.
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.
ARP Learning via Gratuitous ARP
Gratuitous ARP can mean an ARP request or reply.
During ARP learning via gratuitous ARP, 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, the system installs an ARP entry on all three CPUs.
Enabling ARP Learning via Gratuitous ARP
To enable ARP learning via gratuitous ARP, use the following command.
• Enable ARP learning via gratuitous ARP.
CONFIGURATION mode
arp learn-enable
ARP Learning via ARP Request
The system learns via ARP requests only if the target IP specified in the packet matches the IP address of
the receiving router interface. This is the case when a host is attempting to resolve the gateway address.
If the target IP does not match the incoming interface, the packet is dropped. If there is an existing entry
for the requesting host, it is updated.
IPv4 Routing 451