Configuring Dynamic Learning of ARP Entries with Multicast MAC Addresses

Context

An IP address maps to a multicast MAC address in some service scenarios. For example, in Figure 1, the Switch connects to an NLB cluster through the Layer 2 switch LSW. The NLB cluster works in multicast mode and has a multicast MAC address as the cluster MAC address. After the Switch is enabled to learn ARP entries with multicast MAC addresses, it generates dynamic ARP entries based on ARP reply packets from LSW. This reduces a network administrator's workload and decreases network operation and maintenance costs.

Figure 1 Networking diagram for connecting a switch to an NLB cluster through the LSW

Procedure

Globally enable a device to learn ARP entries with multicast MAC addresses
1. Run system-view
  The system view is displayed.
2. Run arp learning multicast enable
  The device is globally enabled to learn ARP entries with multicast MAC addresses.
  
  By default, a device is globally disabled from learning ARP entries with multicast MAC addresses.
  
  If a device is globally enabled to learn ARP entries with multicast MAC addresses, this function is enabled on all the interfaces.
Enable an interface to learn ARP entries with multicast MAC addresses.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run arp learning multicast enable
  The interface is enabled to learn ARP entries with multicast MAC addresses.
  
  By default, if a device is globally enabled to learn ARP entries with multicast MAC addresses, this function is enabled on all the interfaces. If a device is globally disabled from learning ARP entries with multicast MAC addresses, this function is disabled on all the interfaces.
  
  If the undo arp learning multicast enable command is run on an interface, the interface is disabled from learning ARP entries with multicast MAC addresses. Instead, the interface uses the global configuration in the configuration file. If a device is globally enabled to learn ARP entries with multicast MAC addresses, this function is enabled on all the interfaces. If a device is globally disabled from learning ARP entries with multicast MAC addresses, this function is disabled on all the interfaces.
Disable an interface from learning ARP entries with multicast MAC addresses after a device has been globally enabled to learn ARP entries with multicast MAC addresses.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run arp learning multicast disable
  The interface is disabled from learning ARP entries with multicast MAC addresses.
  
  By default, if a device is globally enabled to learn ARP entries with multicast MAC addresses, this function is enabled on all the interfaces. If a device is globally disabled from learning ARP entries with multicast MAC addresses, this function is disabled on all the interfaces.

Verifying the Configuration

Run the display current-configuration | include arp learning multicast command in the system view to check whether the device is globally enabled to learn ARP entries with multicast MAC addresses.
Run the display this include-default | include arp learning multicast command in the interface view to check whether the interface is enabled to learn ARP entries with multicast MAC addresses.