Hi All,
I have a site that is having a problem printing from their printer to their print server. Pings between the two are fine, but users need to make approximately 5 attempts intermittently before the job will go through. This was not a problem until this weekend, when we replaced all of their Dell PowerConnect switches with Cisco 2960 switches.
I did some Wireshark traces, and I am finding that the server is sending the SYN to the printer with the CWR and ECN bits set, which indicate that the transmit buffer on the server is congested. However, when the printer receives the SYN with the ECN and CWR bit set, it RST's the socket. When the buffer is not congested, the SYN comes through without any other flags set and the job goes through fine.
So I am thinking the printer doesn't understand ECN and CWR, which leads me to believe the Dell switches were dropping those bits whereas the Cisco switch is passing them and that is why we have a problem now whereas we did not before on the Dell switches. I have attached the wireshark trace between server (113.58) and printer (111.68). Is there anything I can do in the switch to make it drop the ECN and CWR bits when it receives them so that the printer does not see it? The server team is looking into disabling those flags, but that will be a while.
