arp: unknown hardware address format

[Chuck Swiger]

On Jan 24, 2007, at 4:32 AM, Ilia Gorstkin wrote:
> I'm having trouble with arp:
> arp: unknown hardware address format (0x4500)
> and
> arp: unknown hardware address format (0x4242)
> these messages fall on the console in a plenty.
>
> I do tcpdump -exn "arp[0]=0x45 and arp[1]=0":
>
> tcpdump: verbose output suppressed, use -v or -vv for full protocol  
> decode
> listening on xl0, link-type EN10MB (Ethernet), capture size 68 bytes

Please run "tcpdump -exxn -s 0 arp" to show the full packets  
including link-layer headers.

You should be seeing a byte sequence more like:

0001 0800 0604 0001 ...followed by the sender's MAC address.

This is from /usr/include/net/if_arp.h and means:

ARPHRD_ETHER, ETHERTYPE_IP, hln=6, pln=4, ARPOP_REQUEST

I don't know what 0x4500 means, but 0x4242 is:

#define ETHERTYPE_PCS           0x4242  /* PCS Basic Block Protocol */

It seems more likely that you've got a hardware problem like a wacked  
out NIC or switch, or some really odd software bug...

-- 
-Chuck