Clearing Arp Cache; Arp Learning Via Gratuitous Arp - Dell S4820T Configuration Manual

Clearing ARP Cache

To clear the ARP cache of dynamically learnt ARP information, use the following command.
• Clear the ARP caches for all interfaces or for a specific interface by entering the following information.
EXEC privilege
clear arp-cache [interface | ip ip-address] [no-refresh]
– 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 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 port channel interface, enter the keywords port-channel then a number.
– For a VLAN interface, enter the keyword vlan then a number from 1 to 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.
In the context of ARP learning via gratuitous ARP on Dell Networking OS, 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.
In Dell Networking OS versions prior to 8.3.1.0, if a gratuitous ARP is received some time after an ARP
request is sent, only RP2 installs the ARP information. For example:
1. At time t=0 Dell Networking OS sends an ARP request for IP A.B.C.D
2. At time t=1 Dell Networking OS receives an ARP request for IP A.B.C.D
3. At time t=2 Dell Networking OS installs an ARP entry for A.B.C.D only on RP2.
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IPv4 Routing