Enabling a Device to Learn Multicast MAC Addresses and Generate ARP Entries

If a device is enabled to learn multicast MAC addresses, it can generate ARP entries after receiving ARP packets carrying multicast MAC addresses as source MAC addresses. This section describes how to enable a device to learn multicast MAC addresses and generate ARP entries.

Prerequisites

Before enabling a device to learn multicast MAC addresses, complete the following tasks:

Connect interfaces and set their physical parameters to ensure that the physical interface status is Up.
Configure link layer protocol parameters for interfaces to ensure that the link layer protocol on the interfaces is Up.

Context

A MAC address corresponding to an IP address may be a multicast MAC address. In this case, a network administrator has to configure a static ARP entry. A device can generate dynamic ARP entries if enabled to learn multicast MAC addresses. This way reduces a network administrator's workload of configuring static ARP entries and reduces network operation and maintenance costs.

Procedure

Globally enable a device to learn multicast MAC addresses and generate dynamic ARP entries.
1. Access the system view.
```
system-view
```
2. Enable the device globally to learn multicast MAC addresses.
```
arp learning multicast enable
```
  By default, a device is globally disabled from learning multicast MAC addresses.
  
  If a device is globally enabled to learn multicast MAC addresses, the interfaces of this device are enabled to learn multicast MAC addresses.
Enable an interface to learn multicast MAC addresses.
1. Access the system view.
```
system-view
```
2. Access the interface view.
```
interface interface-type interface-number
```
3. Enable the interface to learn multicast MAC addresses.
```
arp learning multicast enable
```
  By default, if a device is globally enabled to learn multicast MAC addresses, all the device interfaces are enabled to learn multicast MAC addresses. If a device is globally disabled from learning multicast MAC addresses, all the device interfaces are disabled from learning multicast MAC addresses.
  
  If the undo arp learning multicast enable command is run on a specific interface, the interface is disabled from learning multicast MAC addresses but uses the global configuration in the configuration file.
Disable an interface from learning multicast MAC addresses after a device has been globally enabled to learn multicast MAC addresses. The interface does not use the global configuration.
1. Access the system view.
```
system-view
```
2. Access the interface view.
```
interface interface-type interface-number
```
3. Disable the interface from learning multicast MAC addresses.
```
arp learning multicast disable
```

Checking the Configurations

Run the display arp all command to check the dynamic ARP entries corresponding to the multicast MAC addresses.

<sysname> display arp all

IP ADDRESS      MAC ADDRESS     EXPIRE(M) TYPE    INTERFACE   VPN-INSTANCE
                                          VLAN/CEVLAN   PVC                           
------------------------------------------------------------------------------  
192.168.1.1     0002-0002-0002            I -          Vlanif100                 
192.168.2.2     0100-5e11-0302  20        D-0         Eth-Trunk2                
                                           10/-                                
192.168.3.3     0100-5e11-0302  20        D-0         Eth-Trunk2                
                                           20/-                                
192.168.4.4     0100-5e11-0302  20        D-0         Eth-Trunk2                
                                           30/-                                
------------------------------------------------------------------------------  
Total:4        Dynamic:3      Static:0     Interface:1