Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.0P1 - Page 429
Clearing ARP Cache, ARP Learning via Gratuitous ARP, Enabling ARP Learning via Gratuitous ARP, ARP
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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. 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 In Dell Networking OS versions prior to 8.3.1.0, Dell Networking OS 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 429
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