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 Config: Enabled
Get Cmnty Name: Not Specified
Set Cmnty Name: Not Specified
Default Get Cmnty: Enabled
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:
get-request 220.127.116.11.18.104.22.168.22.214.171.124 126.96.36.199.188.8.131.52.184.108.40.206 220.127.116.11.18.104.22.168.22.214.171.124
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?