Will a torrent with no trackers find peers? How long does it take?

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JDLH
Posts: 3
Joined: Mon Mar 18, 2019 7:49 am

Will a torrent with no trackers find peers? How long does it take?

Post by JDLH » Mon Mar 18, 2019 8:21 am

Hello, all,

I have some public-domain content, a movie, which I would like to distribute via the bittorrent protocol. I created a torrent file with no trackers in it. I have the impression that Transmission uses a distributed hash table (DHT) and peer exchange (PEX) to find peers, even without any trackers. Is that a correct understanding? And how long should it take to find a nearby peer using just DHT and PEX — seconds? hours? days?

I am using Transmission 2.94 on Mac OS X 10.11 to create a torrent file and seed it the torrent. My first peer is my file server, on my local network, which runs Transmission 2.94 adapted for the QNAP storage server. Both machines are on the same internal network. Each Transmission instance is set to use a different, non-standard port. I think I have set port forwarding so that both Transmission clients can be seen from the outside: CanYouSeeMee report success at seeing the port.

I had the file server peer upload the torrent file, and start leeching. The Mac peer is running and seeding. I have left both instances to run for over an hour, and neither is aware of the other yet.

Should these peers have discovered each other by now? Are there other ports I need to open to let DHT and PEX work their magic? Would enabling local peer discovery (LPD) help?
    —Jim DeLaHunt, Vancouver, Canada

JDLH
Posts: 3
Joined: Mon Mar 18, 2019 7:49 am

Re: Will a torrent with no trackers find peers? How long does it take?

Post by JDLH » Mon Mar 18, 2019 9:46 pm

I have learned a bit more about how long a torrent might take to find peers.

My Transmission 2.94 instance on Mac OS X 10.11 is clearly talking to peers. I ran Wireshark to capture network traffic to and from Transmission's TCP and UPD ports. There is plenty of UDP traffic between that part and many other IP address:ports. Looking at the packets, they are clearly bencoded as called for in the Bittorrent and Mainline DHT protocols. So I think that instance is finding peers.

Likewise, from my firewall/router I can see there is traffic coming in from many other IP address:ports to both my Transmission instance on the QNAP storage server and the Transmission instance on my Mac.

The Transmission source code mentions bootstrapping DHT from a host, "dht.transmissionbt.com" port 6881. I understand that this host is an entrypoint into the DHT network for a new node. The Transmission code shows it querying this host if all other ways of finding DHT nodes come up empty. It delays 40 seconds before trying, and tries 6 times. So over the course of 2 minutes it has given the bootstrapping node a full chance.

From this, I conclude that an instance of Transmission with open ports and using a trackerless torrent should expect to be talking to peers within hours, maybe minutes, not days.

I haven't figured out how to get Wireshark to decode the bencoded packets, and I'm not very good at reading the hex dumps of the packets, so it's hard to learn more from that at the moment. However, I have hope; Wireshark does know about bencoding.

Wireshark does seem to tell me that there is no traffic between the Transmission ports on my two Transmission instances. Also, the Transmission UIs show that they are solidly stuck at 0 bytes transferred. So, I think that tells me that, although both Transmission instances are talking to peers, they have not yet discovered each other. If anyone has suggestions for how to diagnose that, I would love to hear them.
    —Jim DeLaHunt, Vancouver, Canada

giyadh
Posts: 2
Joined: Fri Apr 19, 2019 11:16 pm

Re: Will a torrent with no trackers find peers? How long does it take?

Post by giyadh » Fri Apr 19, 2019 11:44 pm

hi, im trying to do the same, have you figured out how to create a torrent without trackers? I got it all setup but the file does not download. Doesn't look like its seeing any peers but my other computer is clearly on and has the torrent ready to go.

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