• 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 changeIn the request, the host uses its own IP address in the Sender Protocol Address and Target ProtocolAddress fields.In Dell Networking OS versions prior to 8.3.1.0, if a gratuitous ARP is received some time after an ARPrequest 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.D2. At time t=1 Dell Networking OS receives an ARP request for IP A.B.C.D3. At time t=2 Dell Networking OS installs an ARP entry for A.B.C.D only on RP2.Beginning with Dell Networking OS version 8.3.1.0, when a gratuitous ARP is received, Dell NetworkingOS installs an ARP entry on all three CPUs.Enabling ARP Learning via Gratuitous ARPTo enable ARP learning via gratuitous ARP, use the following command.• Enable ARP learning via gratuitous ARP.CONFIGURATION modearp learn-enableARP Learning via ARP RequestIn Dell Networking OS versions prior to 8.3.1.0, Dell Networking OS learns via ARP requests only if thetarget IP specified in the packet matches the IP address of the receiving router interface. This is the casewhen 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 entryfor the requesting host, it is updated.Figure 36. ARP Learning via ARP RequestBeginning with Dell Networking OS version 8.3.1.0, when you enable ARP learning via gratuitous ARP, thesystem installs a new ARP entry, or updates an existing entry for all received ARP requests.372 IPv4 Routing
