1-6value, the switch considers that the port is attacked by ARP packets. In this case, the switch will shutdown the port. As the port does not receive any packet, the switch is protected from the ARP packetattack.At the same time, the switch supports automatic recovery of port state. If a port is shut down by theswitch due to high packet rate, the port will revert to the Up state after a configured period of time.Introduction to Gratuitous ARPThe following are the characteristics of gratuitous ARP packets:z Both source and destination IP addresses carried in a gratuitous ARP packet are the localaddresses, and the source MAC address carried in it is the local MAC addresses.z If a device finds that the IP addresses carried in a received gratuitous packet conflict with those ofits own, it returns an ARP response to the sending device to notify of the IP address conflict.By sending gratuitous ARP packets, a network device can:z Determine whether or not IP address conflicts exist between it and other network devices.z Trigger other network devices to update its hardware address stored in their caches.With the gratuitous ARP packet learning function enabled:A device receiving a gratuitous ARP packet adds the information carried in the packet to its owndynamic ARP table if it finds no corresponding ARP entry for the ARP packet exists in the cache.If a VRRP backup group exists on a network, the master switch sends gratuitous ARP packetsperiodically to hosts on the network, which then update their local ARP tables, ensuring that no deviceon this network uses the same IP address with the VRRP virtual router.As you can create mappings between the IP address and MAC address of the VRRP virtual router,there are two cases:z If the IP address of the virtual router corresponds to a virtual MAC address, the source MACaddress in the gratuitous ARP packet will be the virtual MAC address.z If the IP address of the virtual router corresponds to an actual MAC address, the source MACaddress in the gratuitous ARP packet will be the VLAN interface’s MAC address of the masterswitch in the VRRP backup group.Configuring ARPConfiguring ARP Basic FunctionsFollow these steps to configure ARP basic functions:To do… Use the command… RemarksEnter system view system-view —Add a static ARP entryarp static ip-addressmac-address [ vlan-idinterface-typeinterface-number ]OptionalBy default, the ARP mappingtable is empty, and entries arecreated dynamically by ARP.Configure the ARP aging timer arp timer aging aging-time Optional20 minutes by default.
