That’s what we faced earlier this week in our Grand Rapids office. It was a mystery as to why all of a sudden a Canon iR-3235 copier would stop working when it came to its “Scan to Folder” function. For Canon, the “Scan to Folder” function opens a CIFS connection to wherever you tell it to go and deposits a scanned PDF file to the destination. Everything up to Monday was working well for us.

After Monday, it was broken. Thanks to a Google Form linked to a Google Spreadsheet I have a handy way to log changes I make to the network in a very convenient way. I open up the form, enter my name and the change, and the Google spreadsheet catches the timestamp automatically. So what changed on Monday? I was using Wireshark and found a flurry of broadcast traffic on using two protocols, LLMNR and NBNS. The first protocol, LLMNR is only useful for small ad-hoc networks that don’t have a standard DNS infrastructure, since we do have a fully-fleshed DNS system running, LLMNR is noisy and superfluous. NBNS is an old protocol, and turning it off system-wide is an accepted best-practice. So I turned off NBNS for all the workstations and turned NBNS off on the servers also. It’s 2016, what could need NBNS?

Then we discovered that our older Canon ir3235 copiers suddenly couldn’t save data to CIFS folders. We verified all the settings, and there was no reason the copiers couldn’t send data to the server, whatsoever, or so we thought. The error from the copier was #751, which was a vague error code and nothing we could find online pointed to error #751 being a protocol problem.

I can’t recommend instituting some change tracking system enough for any other IT shop. Having a log, and being able to pin down exactly what happened and when was invaluable to solving this problem. As it turns out, Canon copiers require NBNS, but not specifically that protocol. When you turn off NBNS on a server, that closes port TCP/139. The other port for CIFS traffic, TCP/445 is used by modern implementations of CIFS. These Canon copiers only use TCP/139. So when I turned off NBNS to tamp down the broadcast traffic, I accidentally made the server deaf to the copiers. Turn NBNS back on, re-open TCP/139, and that fixes these old Canon copiers.