This troubleshooting method uses Address Resolution Protocol (ARP) to check MAC / IP address associations.

From the Web user interface (WUI)

  1. Open the DiagTools tab.

  2. From the Select list, choose arp who-has (interface, source*, destination).

  3. Enter the following parameters:

    • interface: the interface where to send the ARP packet

    • source*: (optional) source IP

    • destination: the destination IP from which to get the MAC address

  4. Click on Run.

From the command line interface (CLI)

  1. Get root rights by typing root.

  2. Run arping -c 5 -I <interface> [-s <source>] <destination IP>.

Output example

ARPING 10.0.32.10 from 10.0.32.11 eth0
Unicast reply from 10.0.32.10 [00:0D:C5:36:C6:72] 0.636ms
Unicast reply from 10.0.32.10 [00:0D:C5:36:C6:72] 0.608ms
Unicast reply from 10.0.32.10 [00:0D:C5:36:C6:72] 0.650ms
Unicast reply from 10.0.32.10 [00:0D:C5:36:C6:72] 0.666ms
Unicast reply from 10.0.32.10 [00:0D:C5:36:C6:72] 0.612ms

Analyze output

In the example above, the MAC address is associated to the IP 10.0.32.10.

Tips

Duplicated IPs

ARP WHO-HAS packets are useful to fix duplicated IPs issues.

When you can reach a server or a VIP on the network, you can use ARP WHO-HAS to check if the MAC address associated with the IP address is the one expected or not:

  • If expected, the problem could be on a upper layer.

  • If not expected, then the MAC address of the server has the duplicated IP