Followup: Netgear missing ARPs

Neale Banks
Wed Jun 30 10:13:16 1999

In relation to the ongoing saga of the Netgear missing ARPs, I think I
have narrowed down the circumstances of this bug and Keith Owens has
identified what's going on at the low levels.  It's really bizzare.

For this to occur:
(1) you have a Netgear FA310TX card
(2) you are on a hub (not switch), i.e. shared media
(3) there *must* be traffic to/from the device you are going to arp (i.e.
the problem goes away if the network is quiet, probably also why it's not
seen on a switch).
(4) you send an arp, and the reply is never seen :-(

What Keith was able to pinpoint was more low-level: when this fault
occurs, all that is to be found in the Netgear's _receive_ ring is a copy
of the arp packet that just went out (i.e. no arp reply, even though
another system on the hub running tcpdump can see it).  

This raises two obvious questions:

(1) what's our own _transmitted_ packet doing in the receive ring?
(2) why is the reply (seen on the wire) not in the receive ring?

These observations were made against the D1 rev of the FA310TX (but I also
had evil experiences with a C-rev of the FA310TX last year which may have
been this same problem).

It only seems to effect ARP packets, something to do with them being
ethernet broadcasts perhaps?

Does anyone else have evidence correlating or conflicting with these

My thanks to Keith for his assistance with this problem.