ARP Diagnostics
This troubleshooting method uses Address Resolution Protocol (ARP) to check MAC / IP address associations.
From the Web user interface (web UI)
Open the DiagTools tab.
From the Select list, choose arp who-has (interface, source*, destination).
-
Enter the following parameters:
interface
: the interface where to send the ARP packetsource*
: (optional) source IPdestination
: the destination IP from which to get the MAC address
Click on Run.
From the command line interface (CLI)
Get root rights by typing
root
.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
Next up
Packet Capture