SNMP and Network Printing

Greetings-

This is more of a theoretical question based on a problem I'm troubleshooting. In our office we have several network printers receiving remote print jobs via the JetDirect protocol over a static IP address. The printer is configured with SNMP enabled with the following configuration (viewing JetDirect settings via telnet):

SNMP SETTINGS:
SNMP Config: Enabled
Get Cmnty Name: Not Specified
Set Cmnty Name: Not Specified
Default Get Cmnty: Enabled

SNMP TRAPS:
Auth. Trap: Enabled
Trap Destination: (blank)

We want to install a hub between the printer and the switch, in order to capture incoming network traffic using Wireshark. Once the hub is in place the network connections are as follows:

(1) [Uplink] connection to the switch
(2) Connection to the network printer
(3) Connection to the Linux machine running Wireshark

The connections all appear to be correct and pings between all 3 connected devices are successfully sent and returned. Furthermore, I'm able to telnet into the printer configuration menu with the same result as before the hub was installed.

The problem I'm running into now is that with the hub in place the printer fails to received and process the incoming remote print jobs I'm interested in. As soon as I eliminate the hub print jobs are processed as normal. When I look at the Wireshark traffic during periods in which the hub is connected, instead of seeing the initial SYN packet to port 9100 signifying the start of the print job I see the same unanswered SNMP get-request packet:



Basically the same SNMP get-request packets are sent to the IP address of the network printer. Of course the printer fails to ever send a response.

Any suggestions on where to begin in order to try and understand what's going on here?

Thanks.

Instead of throwing the hub in there can you do a port-monitor from the switch itself? It acts just like a hub with the collision domain aspect. I'm wondering if there's a goofy auto/auto for the speed/duplex error that's preventing the printer from working correctly. I'd try either the port monitor on the switch itself if you can, then maybe try hard-coding the printer to use 10/half for now.