Transmission – Port is closed

I don’t often get into 3rd-party software or non-Mac hardware issues, but here’s a little trick I discovered today that could prevent a situation that adversely affects Safari and other network software.

Not so long ago I bought a new router, and everything was working fine. However, when I recently fired up Transmission, I found that not only were my downloads not so fast as I’d normally expect, but that all internet browsing was completely throttled. Basically, Safari would just get stuck half way into loading a page and eventually timeout. Killing Transmission would immediately restore Safari’s connectivity.

Looking in Transmission’s preferences ‘Network’ pane revealed that the port was either closed (red button) or the port could not be checked (yellow button). Now there are a number of reasons this can happen, but since I knew nothing had changed except my router since the last time Transmission was successfully used, I decided to go check out some of the router’s settings.

To do this, quit Transmission if it’s running, then enter your router’s IP address in Safari’s search bar. Typically, this will be something like 192.168.1.1, but if you’re not sure, you can find your router’s IP using my free utility ‘FastTasks‘.

Once you’re in your router’s admin pages, look for Advanced network settings. In my router, I found a bunch of firewall and network protocols (see the first screenshot below). Neither disabling NAT nor UPnP had any effect (those were my first thoughts about the likely culprit), but turning off the ipSec PassThrough option sure did, with the upshot that Safari and Transmission are not only playing nicely together again, but Transmission’s download speeds have markedly improved. 🙂

Here’s the settings I used to get back up and running; see if you can find similar options if you’re experiencing the same problem.

Turning off ‘ipSec PassThrough’ in my Router’s Advanced Settings:

Transmission’s Network Preferences pane:

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