Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 466

www.dell.com | support.dell.com 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. Beginning with version 8.3.1.0, when a Gratuitous ARP is received, FTOS installs an ARP entry on all 3 CPUs. Task Enable ARP learning via gratuitous ARP. Command Syntax arp learn-enable ARP Learning via ARP Request Command Mode CONFIGURATION In FTOS versions prior to 8.3.1.0, FTOS 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, then the packet is dropped. If there is an existing entry for the requesting host, it is updated. Figure 24-1. Learning via Gratuitous ARP VLAN ID: 1.1.1.1 ARP Request Target IP: 1.1.1.3 X Host 1 IP: 1.1.1.2 MAC: AA Target IP is not the VLAN interface IP. Update existing Host 1 entry. Drop packet. Host 2 IP: 1.1.1.3 MAC: BB 466 | IPv4 Addressing