Kernel: arp: unknown hardware address format (0x4d6f)



  • A strange line is added to the system log (Status: System logs: System) several times a day:```
    kernel: arp: unknown hardware address format (0x4d6f)

    
    Googling shows that, indeed, there is no known EtherType with 0x4d6f value, and such a message is believed to be caused by malfunctioning hardware somewhere in the LAN. But the funny coincidence is that all reported values are all the same: the most popular is 0x4500, then goes 0x0000 followed by 0x4242, as well as the notorious 0x4d6f. Only one report that I found was about really random (ever changing) values.
    
    Unfortunately, pfSense not only omits additional information about the malformed frame, but doesn't even include any hint on which interface this frame was received. So I added _shellcmd_ directives for all the interfaces (except loopback):```
    /usr/sbin/tcpdump -i {interface} -exn "arp[2]=0x4d and arp[3]=0x6f" > /var/log/arp_{interface}.log &
    ```Surprisingly, those log files are still empty, while the system log still gets filled with messages. (The files _are_ filled when condition is changed to 0x08+0x00 for regular IPv4 announcements.)
    
    So the question is either:
    
    *   How to debug this?
    *   How to disable this message from being logged?
    
    The second option is the most interesting, as many software tend to exaggerate really insignificant problems.

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