Fin flag set mid-transmission
Posted on 2009-04-02
Problem: PC sends large job to printer via LPR. The source of the job is a file on the PC's local drive. Resulting printer output is only part of the expected output. No errors apparent on either side. Traffic is on local network within building, with only a switch in between.
Troubleshooting: Ran Wireshark capture to see if I could determine what was happening. The problem appears to be caused by the PC sending the job. On both occasions when I have managed to capture this, one packet from the PC has the FIN flag set (actually, FIN, PSH and ACK). But, the data in the packet is from the middle of the print job. When the printer receives the FIN, it procedes to acknowledge the end of the connection. I have checked to make sure that the file on the local drive is the complete file. There are no obvious transmission problems (no retransmits, no too fast retrans, no duplicate acks, etc). The only thing that has occurred, in both cases, was a period of zerowindow traffic shortly before the FIN packet. But, the zerowindow situation resolved normally, and the packet transmission had resumed. I have researched to try to find why this might happen, but I'm at wit's end. We have updated the driver on the PC's NIC. Any advice is greatly appreciated.