["Julian Fielding" <jfielding@xxxxxxxxxxxxxxx>]

jgt@xxxxxxxxxxxx on Mon, 20 Sep 2004 12:35:26 -0400 said
>Currently all I am able to see are Class 1 Output data messages that are transmitted by the field device.

I think your hub is really a switch. Or it's a dual-speed hub and your Ethereal connection is at a different speed from the EtherNet/IP devices. Class 1 messages from a field device (which are more correctly called input messages - the CIP convention is that the terms "input" and "output" are used from the PLC's point of view) are UDP multicast (typically). The output messages (from PLC to field device) are UDP unicast. Explicit messages are TCP (unicast). A switch (or the switch between the two speeds of a dual-speed hub) will only give you the multicast messages.

I use Ethereal with EtherNet/IP frequently with no problem. I have a genuine hub. These seem to be quite rare now. The alternative is a switch that lets you configure one port to monitor another.

I apologise if I've jumped into the middle of a conversation. My company's email system seems to be blocking most messages from Ethereal lists at the moment, and the list archives show nothing for September, so I couldn't check.

Julian.