Transmission Port Closed [Possible Solution SOLVED]

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spacewrench
Posts: 3
Joined: Sun Jun 17, 2018 5:38 pm

Transmission Port Closed [Possible Solution SOLVED]

Post by spacewrench » Sun Jun 17, 2018 5:54 pm

I just dug into a "port closed" problem for transmission-daemon on a Linux machine. The port was definitely open (according to canyouseeme.org and other testing methods), but transmission-daemon couldn't confirm it.

Here's what I learned from looking into the source code:

Transmission-daemon (and probably the other transmission-xxx programs) checks whether remote peers can talk to it at a port by sending a request to http://portcheck.transmissionbt.com/{your-port-number}. This server tries to talk to a BitTorrent client at your apparent IP address and port, and returns 1 if successful, 0 if not.

The problem I was seeing was, the machine where my transmission-daemon was running, had an auto-configured IPv6 address (as well as an IPv4 address). When transmission-daemon accessed portcheck.transmissionbt.com, it was using IPv6, and portcheck.transmissionbt.com returns a 400 Bad Request response to that. When I disabled IPv6 on the machine, everything started working right.

My upstream ISP is Comcast, and I have a static IPv4 address allocated. However, the cable modem also auto-configures IPv6, and some of my computers use IPv6 when possible/available.

I don't know whether the problem is due to weird Comcast IPv6 handling/routing, incorrect IPv6 handling at portcheck.transmissionbt.com, or some other problem. But if you're having trouble with "Port Closed," this is something to check.

josephj
Posts: 95
Joined: Wed Mar 25, 2009 6:46 pm

Re: Transmission Port Closed [Possible Solution SOLVED]

Post by josephj » Tue Jun 19, 2018 5:50 am

I was wondering about that myself. Thanks. (Now, if I can figure out how to disable IPv6 ...)

rikki
Posts: 1
Joined: Thu Nov 01, 2018 2:43 am

Re: Transmission Port Closed [Possible Solution SOLVED]

Post by rikki » Thu Nov 01, 2018 2:51 am

Launched AirPort Utility.app, selected my AirPort Extreme, clicked on Edit, selected Internet tab, clicked on Internet Options..., in Configure IPv6: select Link-local only.

spacewrench
Posts: 3
Joined: Sun Jun 17, 2018 5:38 pm

Re: Transmission Port Closed [Possible Solution SOLVED]

Post by spacewrench » Sat Dec 29, 2018 9:45 pm

Same problem appeared again...I found a configuration line in /etc/transmission-daemon/settings.json for "bind-address-ipv6" ... deleted this and it started working, but it also automatically re-added the line (transmission-daemon updates and rewrites the settings file on the fly). I don't know if there's a reliable, permanent solution to this.

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