432 | IPv4 Routingw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Beginning with version 8.3.1.0, when a Gratuitous ARP is received, FTOS installs an ARP entry on all 3CPUs.ARP Learning via ARP RequestIn FTOS versions prior to 8.3.1.0, FTOS learns via ARP Requests only if the Target IP specified in thepacket matches the IP address of the receiving router interface. This is the case when a host is attempting toresolve the gateway address.If the Target IP does not match the incoming interface, then the packet is dropped. If there is an existingentry for the requesting host, it is updated.Figure 20-8. Learning via Gratuitous ARPBeginning with FTOS version 8.3.1.0, when ARP Learning via Gratuitous ARP is enabled, the systeminstalls a new ARP entry, or updates an existing entry for all received ARP requests.Figure 20-9. Learning via Gratuitous ARPWhether ARP Learning via Gratuitous ARP is is enabled or disabled, the system does not look up theTarget IP. It only updates the ARP entry for the Layer 3 interface with the source IP of the request.Task Command Syntax Command ModeEnable ARP learning via gratuitous ARP. arp learn-enable CONFIGURATIONHost 1IP: 1.1.1.2MAC: AAHost 2IP: 1.1.1.3MAC: BBARP RequestTarget IP: 1.1.1.3Target IP is not the VLAN interfaceIP. Update existing Host 1 entry.Drop packet.VLAN ID: 1.1.1.1XHost 1IP: 1.1.1.2MAC: AAHost 2IP: 1.1.1.3MAC: BBARP RequestTarget IP: 1.1.1.3Target IP is not the VLAN interfaceIP. Install new entry for Host 1, orupdate existing Host 1 entry.Drop packet.VLAN ID: 1.1.1.1ARP Learning via Gratuitous ARP enabledX
