Which connections are provided through UDP?

[LovesTheSun]

Is there a way to see which connections, during download, are provided through UDP?

Bc. I'm curious how much this DHT/UDP is really helping my downloads.

DHT and UDP-trackers are providing a lot of peers when I look at the trackers-tab in BC, more than the TCP trackers provide.

But when I remove the UDP-trackers and block my UDP-port I still get the same peer results/download speed.

Edited November 3, 2010 by LovesTheSun (see edit history)

[kluelos]

No connections at all take place via UDP.

DHT uses UDP (exclusively) to maintain a database of peers, and to send a list of peers interested in a particular torrent when queried, but it is up to those peers to contact and form connections with each other. That connecting is done separately by the clients, doesn't involve a tracker, and happens via standard http file transfers.

The (very!) few trackers which are set up to also use UDP provide exactly the same information via http. I am aware of no tracker that uses UDP only. µtorrent refused, at least in prior versions, to support UDP at all, so it would not use such a tracker if such existed.

Therefore, when you have both the TCP (HTTP) and UDP versions of a tracker, you are just hitting that tracker twice for exactly the same information, gratuitously doubling the load on the tracker to no benefit at all.

(Many torrents list UDP urls that simply do not exist and never have. Many torrents list UDP urls that are just duplicates of HTTP urls, added by the creator in a sort of fuzzy thoughtlessness. This is foolish, useless, and where it is not useless it is harmful to the tracker to hit it twice.)

All of the peers from all of the sources (trackers, DHT, PEX) go into a common "bucket" from which the client draws. How they got into the bucket is irrelevant to the ongoing process of contacting and negotiating with each other. How they got into the bucket is really almost meaningless anyway.

Generally, if you download a torrent that lists 5 trackers and isn't private, then you start that task, you will be contacting the 100 other peers who downloaded that same torrent and polled to those same 5 trackers plus DHT, plus PEX. Knock one tracker out of the situation (it went down, or it's UDP and you decide to block UDP), and now the same group of peers including you is talking to 4 trackers, DHT, PEX, with no net difference at all. If you block UDP then you don't poll that one UDP tracker, but you get the same list of peers from the other 4 and from DHT anyway.

If one particular client is listed by four trackers, and also listed in your DHT results, to which of those would you fairly "attribute" that peer? Where did he "come from"? And what difference does his origin make to you or to him? You're not going to treat each other any differently based on how you found each other, even if you did attribute that somehow, fairly or not. See? Meaningless.

So why use DHT at all? In previous years, it was common for trackers to go down and stay down. (That still happens, though less often now.) When it did happen, the peers were simply stuck with transfers that would never finish and no way to find each other. However, with DHT (which is entirely independent of any tracker), the peers can continue to find each other and exchange pieces, so even if all of the trackers go down, the transfers continue. ThePirateBay took down its tracker permanently and completely some months ago, so peers using its torrents rely entirely on DHT and PEX to find each other.