Dell Force10 S55T S55 Configuration Guide FTOS 8.3.5.3 - Page 339
ARP Learning via Gratuitous ARP
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Command Syntax clear arp-cache [interface | ip ip-address] [no-refresh] Command Mode Purpose EXEC privilege Clear the ARP caches for all interfaces or for a specific interface by entering the following information: • For a 1-Gigabit Ethernet interface, enter the keyword GigabitEthernet followed by the slot/port information. • For a port channel interface, enter the keyword port-channel followed by a number from 1 to 255 for TeraScale and ExaScale. • 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. E-Series ExaScale platforms support 4094 VLANs with FTOS version 8.2.1.0 and later. Earlier ExaScale supports 2094 VLANS. 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. 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. In FTOS 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 FTOS sends an ARP request for IP A.B.C.D 2. At time t=1 FTOS receives an ARP request for IP A.B.C.D 3. At time t=2 FTOS installs an ARP entry for A.B.C.D only on RP2. IPv4 Addressing | 339
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