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I have been experimenting with an application that listens to network ports below 1024.

I discovered that when that application is running, an attempt to print to a network printer (set up to print using LPD) will get stuck at "Printing - Connecting to printer". To be clear, the client is running the test application listening to sockets below 1024 and can't send print jobs to an LPD-enabled print server.

I've tried configuring the test application to not listen to ports 631 and 515, but still the print job gets stuck. Killing the test application allows printing to work fine.

My question is: when trying to print to a network print server using LPD, what ports below 1024 have a printing-related process connect to them? I want to "whitelist" them from the test application so printing works while the test application runs.

This is being done on OS X 10.10.3

  • knowing which test app you're using may help – Tetsujin Apr 24 '15 at 17:55
  • You may want to try ports 721-731, based off of information from: members.cruzio.com/~jeffl/sco/lp/printservers.htm "515 TCP port for LPD. This port can be used when printing with LPD (for example, from UNIX (R)) or using LPD emulation like the Microsoft (R) LPR port monitor. While port 515 is the listen or destination port, TCP ports 721-731 are the source ports on the host machine." – smoooosher Apr 24 '15 at 17:59
  • @smoooosher It looks like if I exclude that range it works! Thanks! If you have it as an answer, I'd accept it! – Bart Silverstrim Apr 24 '15 at 21:54
  • @BartSilverstrim Glad that it worked for you! I updated with the answer as you have verified that it is working. – smoooosher Apr 24 '15 at 21:57
  • I did a little poking/testing, and it looks like as long as nothing is listening on the 721-731 range, it would print in my test cases. 515 must be just for servers; re-adding that to the listening list didn't stop test print jobs from sending to the server. – Bart Silverstrim Apr 24 '15 at 21:58
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You will want to try excluding ports TCP 721-731 as these tend to be the source ports for printing. TCP 515 is the listening port for LPD jobs.

Source (in the FAQ/questions section at the bottom)

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