PEX protocol (peer exchange) questions

[Ramalama1]

I read everything I could find on the subject but ended up with more questions than I started out with.

First, I thought that PEX was not the same across clients so that our version is not the same as say Azureus's version.

Second, I thought that PEX only worked across the same domain or ISP.

Today I downloaded two torrents from the same private tracker. One arrived with PEX enabled and one without. Thinking back to what I read, I disabled PEX in the job that had it only to discover, to my dismay, that the only peer that has 100% was discovered through PEX and that by disabling it I snubbed that peer. OUCH. Well the actual person was not snubbed, just their computer so I guess it isn't all that bad. Having discovered this error on my part I renabled that peer via PEX and am now happily downloading from him/her. I know that from the peer info. that this is not someone on my network or provider - this person is not even in the same country as me. Incidentally, the PEX enabled torrent is not on the current port that this particular tracker asks that we use to upload new .torrents to.

Can someone fill in the blanks for me?

[DreadWingKnight]

First, I thought that PEX was not the same across clients so that our version is not the same as say Azureus's version.

Nope, There's a standard in accepting the protocol.

Second, I thought that PEX only worked across the same domain or ISP.

Not even close. It matches across all peers you're connected to.

[GTHK]

I get the impression you're also thinking of LPD, Local Peer Discovery, which uses multicast and can thus only work locally. And DHT, which Azureus uses an incompatible version of. PEX allows clients to exchange known peers. More info: http://en.wikipedia.org/wiki/Peer_exchange

Based on that article, it seems Azureus works with µT's PEX, it's Azureus' DHT that's incompatible. Also, PEX, DHT, and LPD are disabled if a torrent is flagged as private.

[Ultima]

Even if Azureus DHT is incompatible, Azureus is still able to connect to mainline DHT via a plugin

the only peer that has 100% was discovered through PEX and that by disabling it I snubbed that peer

Well, "snubbed" isn't the word you want to use here, since PEX doesn't affect snubbing "By disabling it, you lessened the chances that you'd connect to the peer automatically" is what you want to say ;D (Snubbing has a precise definition in BitTorrent)

[Ramalama1]

AHA! (smacks forehead) and exalt to you GTHK for pointing out what should have been obvious - too much reading makes for a cluttered brain - too many new concepts. Considering that I only started using this protocol less than a week ago, maybe I am trying to get up to speed to fast.

Now that I can actually ask an intelligent question, when you upload a .torrent to a private tracker such as Demonoid, you cannot enable PEX since it must be tagged as private. So how in the world did I get a .torrent with PEX enabled from Demonoid?

Thanks for the link, I read that, it did help. And thanks DWK, for clearing up some more of the cobwebs.

ETA @Ultima - I got that term from looking at the errors in the log and by looking up the Flag codes.

Well, "snubbed" isn't the word you want to use here, since PEX doesn't affect snubbing "By disabling it, you lessened the chances that you'd connect to the peer automatically" is what you want to say ;D (Snubbing has an exact definition in BitTorrent)

more homework...

[Ultima]

You can check the glossary in the manual for definitions. There's also the more traditional link here for the basic BitTorrent jargon

(It's nice to see someone willing to learn/understand BitTorrent every once in a while )

[GTHK]

Additionally, Demonoid is more a semi-public tracker, you don't HAVE to private flag your torrent, I guess people do it anyway to prevent moochers from avoiding ratio related stuff, even though a minimum ratio isn't enforced either (read Demonoids FAQ).

[Ramalama1]

I took a look again at D's FAQ - nice of them to use uTorrent as their example, eh?

In the create torrent section it says to check private but I never tried not checking. I have noticed that there are some evident changes in the FAQ since they came back online so perhaps they changed this. Not sure, but even if they did, the .torrent I d/l'd was an old one from before the hiatus.