*UPDATED* BitComet F.A.Q.s [Still in Progress]

BitComet Guides and Tutorials
1

BitComet - Frequently Asked Questions Section

Last Updated: Thursday, 24th April, 2008

Users, please do not post within this topic.

This will be our new BitComet FAQ Page. We sincerely express our thanks to Dragosani and his team, at P2P, in helping us answer all BitComet Related Questions.

Should your question not be answered in this FAQ please post in:

BitComet Client General Help - Only BitComet issues
BitComet Client Bug Report - Parts of BitComet not working? Submit here.
BitComet Client Feature Requests & Suggestions - Want some new features in the future BitComet release?
Port Forwarding & Router Setup - Only for Router and associated issues.

BitComet User Interface

This is my first time using BitComet as well as torrents, so how do I use it?

I’m only seeing either of these two icons: or
What do the icons next to the task mean?
What’s the meaning of “disconnected0” “disconnected1” “disconnected2” Peer tab → Status?
What is .bc! next to my filename?
How do I change my default directory?

BitComet Client Issues & Possible Solutions

What’s this red cross that appears next to my torrent?

What is DHT? How come I have “DHT not Connected”

How come the speed located at the top of the BitComet client states a different speed to my overall torrent downloads?

I’ve found out that my ISP has throttled my bandwidth since I was using P2P software, what should I do?
I want to open the torrent sites within BitComet with my own web browser
How do I reset my Login Password for BitComet (Latest versions only)
Torrent Already Exists Error

Configuration & User Settings

Up-to-Date BitComet Speed Guide

My internet runs through a router, and since I installed the router, my speeds are so slow for BitComet

BitDave’s BitComet Settings Guide

My BitComet settings reset by itself everytime I re-open the client
Questions regarding BitComet Settings?

How to Open Ports in Windows Vista

Known Client Issues & Incompatibilities

I’m using BitComet 0.6x, 0.70 and my PC seems to crash alot - If this occurs, uninstall BitComet, and install older versions such as 0.64
Norton Antivirus continues prompting BitComet to permit / decline
BitComet uses ALOT of my memory (i.e. CPU Processes) and I’m also using an Nvidia Firewall
PeerGuardian/Protowall Users Conflict with BitComet

Torrent Related

I’ve just finished my torrent download, what are all these files inside the torrent’s directory? (i.e. so many numbered files, .iso, etc)
My torrent download is stuck on 9x.x% / 98.x% / 99.x% What should I do?
How come I’m downloading so much rubbish data. In fact, what is rubbish data?

What are Private or Public Trackers?

I’m receiving tracker errors within a torrent I’m downloading

FAQ Compiled by Soraiya & Sources have been noted.

faq_01-1.png

2

A red cross appears next to my torrent currently being downloaded in BitComet. What is it?

This red cross generally means that BitComet cannot continue transferring this file because:

BitComet can’t write to the disk, or
BitComet can’t read from the disk.

(Depending on your BitComet version, you should try mousing over the X to see if you can obtain specific information about the problem.)

**Solution: **

Many things can prevent disk reads or writes. The most common cause is that the account BitComet is running under lacks the needed directory or file permissions. Invalid characters, nonexistent pathnames, and disk errors are some of the possible causes.

Torrent Sharing

If you are attempting to download a shared torrent when you get the red X, this can mean that the peer who was sharing the torrent has disconnected, and BitComet cannot find any other sharers with the same torrent. In this case you can try again later or select a different shared torrent.

3

I’m only seeing the or icons next to my torrent’s name.

The icon means that the tracker(s) you’re connecting to has timed out or is otherwise currently unavailable; or that the torrent is trackerless.

This icon means that you’ve successfully exchanged metafiles with the tracker, and BitComet is currently attempting to connect to Peers/Seeders for you, but has not done so yet. This icon usually changes to the green down-arrow very quickly.

Solution

→ Try enabling your DHT network as well, by right clicking on that torrent, Click Properties, Advanced, Under Task Settings → Click the checkbox “Enable Public DHT network”.

→ Try enabling your DHT network [instructions above]. In normal torrent downloads, you should see this icon only for a split second, it should then change to the green arrow facing downwards. If you continually see this icon for more than an hour or so, it’s more than likely that the torrent no longer has peers/seeders, OR if you’re suddenly seeing this icon appear during your torrent download, it means that no peer has your remaining data (Check your peers tab, and see whether other users also have the same download percentage as you do). This icon can also occur if your internet connection has terminated for some reason.

4

In my trackers → Status tab, I’m seeing errors like 18:16 Can’t connect to tracker (110004), waiting 1800s to retry, or Can not resolve host address [shown below]:

Solution

Unfortunately there isn’t any solution to this issue, because it is the tracker itself that’s down or unavailable. Try stopping and restarting the torrent download, to try and re-connect to the trackers. If the trackers are all unresponsive, be sure to use the DHT network to connect to peers [Right-click on the torrent → Properties → Advanced → click the checkbox Enable DHT network].

If your internet connection is configured to redial if the line is dropped (Meaning if your internet disconnects, it will automatically re-dial by itself), and if your internet does indeed disconnect, and redial by itself, BitComet may be unable to connect to these trackers. This can be resolved by disabling your Internet Connection, and re-enabling it, then opening BitComet to resume the downloads.

If the tracker gives the status: “Can not resolve host address.” Then this is mainly because you’re using BitComet’s UDP trackers, these rarely work unfortunately. Try using public trackers such as

http://tracker.prq.to/announce
http://tv.tracker.prq.to/announce

Registration at Demonoid.com and torrentbox.com will also allow you to use their torrent trackers.

BitComet’s UDP trackers are usually only used for uploading BitComet torrents i.e. setup files, etc.

5

What’s the meaning of “disconnected0” “disconnected1” “disconnected2” Peer tab → Status?

This is nothing to be of concern to your torrent downloading activities. This tells you how many times the client has failed to connect to that peer.

6

I’m at xx.x% right now, and in my “Downloaded: XX Mb (x B Rubbish Data)” part, I’m getting alot of rubbish data. What is it?

Solution

Rubbish data is simply caused by peers sending bad packets to the swarm. Whether intentionally or unintentionally, we’re still not sure. It could either be caused by peers having bad connections to the tracker, as well as a variety of other things, as well as so-called government companies which are able to mingle into the swarm and release bad data intentionally so as to hinder torrent users.

The only solution so far to this problem is to download Peer Guardian: http://phoenixlabs.org/

Download and install the client, and when it comes to the screen of ‘Updates’ click on the checkboxes: Government, P2P, Ads. Then let PeerGuardian update its lists. Allow PeerGuardian to run everytime your BitComet client is functioning.

A reminder to users: This program does not guarantee that you will receive nil rubbish data, or that you’ll be “protected” from governmental agencies trying to obtain your IP address. Alot of users are under the general idea that some clients are able to block all rubbish data, we can assure you that this is not true. The most that it can do is limit the amount of rubbish data being passed through to your torrent downloads.

However, personally I find that whenever I use Peerguardian or Protowall alongside any P2P applications, it seems to limit your download capability especially for torrents that connect to remote peers.

7

How come the speed located at the top bar of the BitComet client states a different speed to my overall torrent downloads?

There is no real solution for this, and it’s not really an error. The speed you’re seeing at the top of the client is actually the instantaneous speed of your DHT network & tracker establishment speed, in other words, without the technical jargon: This is the projected (predicted) speed of your overall torrent downloads, but not necessarily your real overall torrent download speed.

Hence, this is the reason why the overall speed may match the real overall speed of your torrent downloads.

Solution

Dragosani from the P2P Forum has offered a solution which may solve this error:

Go to Options > Preferences > Advanced > Connection > “Use NAT Traversal via UDP” [disable]

Whist other members have disabled NAT transversal via UDP

[Contributed by DarkShroud, Dragosani, and users from P2P - BitComet forum]

http://www.p2pforums.com/viewtopic.php?t=13862

8

Question: My ISP has throttled my bandwidth! Because they’ve found out that I was using P2P downloads.

Solution

Obviously, the best solution is to change your ISP as soon as possible! You do not want to waste $70 on some 20 mb connection, if you’re now only using 2 gigabytes out of your 50 gigabyte download quota. Because simply, there are alot of other ISPs in the market who care only about the money. You as a consumer pay them $ and they will in return provide you their service.

Alternatively, if you’re stuck on a contract with your ISP or do not wish to switch, try out our encryption technology:

You can enable this encryption protocol within Bitcomet by following these steps:

Open BitComet (ensure that its not an old version like 0.60 or below) to: Options → Task → BitTorrent (or Options–Advanced–>Connection in older versions).
Locate “Protocol Encryption” Here you can choose between ‘auto-detect’ or ‘always’. Always is a safer option for users who are fully aware that their under ISP throttling. For those who aren’t sure, use ‘auto-detect’ first, this allows your client to receive more connections, but may lead to lower encryption.
Our Recommendation is for to use “Auto-detect” first, if you do not find any change in speed, then use ‘always’.
It should look like this:
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or like this (in older versions):

9

Difference between Private Trackers & Public Trackers. It’s important to understand however that bittorrent is a network completely different to Kazaa or Shareaza, in that people who download the torrent must at the same time upload their data to other peers, and the most fundamental rule of all torrents is “The higher your upload capability is, the better your download capability will be.” [For more information on how to maximize your download speed with BitComet, please read our Official Speed Guide (This has not been officially released, as the BitComet team is still compiling it]

Public trackers are tracker urls which are made public, or in other words, torrents with this type of tracker allows ALL users to both access and download this torrent’s contents. As a result:

Users with ‘Hacked’ torrent clients or clients with add-ons are able to optimize their ‘own’ download capabilities, which in turn harms the swarm of peers in your torrent download.

Seeders (Users who hold the completed torrent file(s)) have no obligation to continue uploading their data to peers. So the Seeder to peer ratio is extremely low.

Leechers have no obligation to upload their data as soon as their file is completed.

E.g. isohunt.com torrenspy.com mininova.org

Private Trackers are tracker urls which are private, users must register at their home site to be able to access both this site’s torrents and tracker:

A Download to Upload ratio is inplace for every single user who registers at that site. With that users Download to upload ratio, the site controls the number of hours required before the user can access that torrent via the site’s tracker.

People with bad D:U ratio will be kicked off the site

All users within that private torrent community can enjoy downloading the latest releases of movies, games, programs, applications, animations with maximised speeds (Please note however, this also depends on your upload speed again. So the better your upload capability is, the better your ratio and download capaibility will be for the torrents on that site.

Filelist.org, Midnight torrents, etc [search via Google - Private torrent community/site]

10

BitComet Version 0.68 - For some reason, everytime when I open BitComet, all my settings are reset, what’s happening?

Solution

[Direct Copy & Paste - Contributed by kluelos ]

Something has either opened the settings file or changed its properties.

The file is “bitcomet.xml” and it’s located in your program directory, nominally c:\Program Files\BitComet

Find the file, right-click on it and check the properties. If Read-Only is checked, uncheck it and try again. That should solve it.

If it still doesn’t work, something is holding the file open, and you’ll need to find out what, and why. The “why” is very important because it shouldn’t be happening. Get a free tool named “Unlocker” and use it to find out what’s latched on to the file, and determine if you can safely unlock it or kill that process.

11

I want to revert to an older version of BitComet because my current version BitComet 0.6X i.e. most likely versions 0.68,0.67 are encountering crashes. I’ve uninstalled 0.68, 0.67 versions but I’m still crashing.

Partial Solution

In order to revert back to a clean BitComet install, please do the following:

Uninstall BitComet

Head to the BitComet installed directory and delete all the contents there.

Then delete your ‘bc_cache’ file contents: Its locations in 9x/me & XP: c:\windows\temp\bc_cache\

or

c:\documents and settings\local settings\temp\bc_cache\

Once both of these are deleted/uninstalled, try installing BitComet 0.64 or 0.63. Please remember that by doing this, all torrent information in your currently installed BitComet client will disappear. You will need to re-open the torrent, find the torrent’s partial download location, and do a manual hash check to allow BitComet to be aware that you have a partial download.

12

I want to open the torrent search engine sites (located within the favourites tab of the BitComet client) with my PREFERRED web browser i.e. Mozilla firefox.

Solution

  1. Options → Preferences

  2. Appearance → “When BitComet is running” → Unclick the checkbox “Open URL inside BitComet”

  3. Now whenever you double-click the torrent search engine sites within our client’s favourite, it will open up with your preferred web browser i.e. Firefox.

13

The Private torrent community banned my BitComet client, what should I do?

Solution

Firstly, lol please don’t listen to the general rumours or questions like “Tired of being banned by Private trackers, try Utorrent”. The solution to this is extremely easy, download another BitComet version which is NOT 0.59, 0.60.

Most other versions like 0.61 and onwards should suffice, and work with the private trackers. If only and only if the private torrent community you’ve joined inhibits all BitComet client users, then switch your client.

Please note: If your private torrent tracker doesn’t allow recent versions of BitComet, I suggest you politely ask them to review the topic in Announcements titles “Examining the Myths and Facts about BitComet”. This is an independent report and demonstrates that the rumors are not based in fact.

The BitComet team is very Grateful to this member of the community who took it upon himself to research these issues, and offer his research to the community.

14

Torrents stopping at 99.x%

This issue happens very commonly with all P2P applications for several reasons.

If you are using a router, be sure to DISABLE the dmz function within your router, this function is normally used for online gaming purposes rather than torrent clients.

Disable the gaming option within your router if you have it. As most routers enable such functions by default.

Disable/Close Firewall-software based.

This final option is ONLY done at your risk → Disable your Router’s Firewall and/or NAT function (If you’re unsure of whether you have NAT NAT test

Finally, if all of the above does not work, you will need to verify whether or not you are downloading a ‘Fake Torrent [1]’. You can verify this simply by going into your Peers Tab on BitComet, and having a glance at the general trend of peer percentages. You should look particularly at the xx.x% that users are stuck on i.e. 98% or 99.8%. Here, a further 2 scenarios are created:

  1. If there are ** 0 ** Seeders (i.e. People with 100% of that torrent), then this is not a fake torrent, rather a non-working torrent, where all the seeders have left, or the torrent itself may be quite old. If this is the case, have patience, and let the torrent run for at least 1 more week. If no seeder returns, look for another similar torrent to the one you’re downloading.
  2. If there are ** More than 2 or 3 Seeders (i.e. People with 100% of that torrent)**, but also a large number of people stuck on a certain percentage say 99.8%, then unfortunately you have downloaded a fake torrent. No matter how long you leave the torrent running, you most definitely will never complete the torrent, rather you will be wasting your bandwidth away on Rubbish data[2]. Try finding another torrent. If the torrent you’re trying to download simply contains .avi or .mpeg files, try opening them direct with Windows Media Player.
    Short Glossary
    [1]Fake Torrent: The distribution of fake torrents has started to become a rather irritating issue, but one that alot of torrent search engines are dealing with at the same time. Fake torrents are those that utilise fake trackers that intentionally reports fake information such as Peers (more Information here: <a href=“http://p2pnet.net/story/6362" target=”_blank">http://p2pnet.net/story/6362 ). These torrents usually attract alot of users into downloading it, and in doing so, you may actually receive max download speeds, but in turn, you may download a heap of rubbish data[2].
    [2]Rubbish Data: This is ‘corrupt’ or ‘bad’ data/packets sent by peers. You can Reduce the amount of Rubbish data being downloaded
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Known Conflicts with BitComet and Incompatible Routers

The Following Routers are known to have conflict with our Client (as well as Azureus):

D-Link DI-624

DI-624+

DI-604

D-Link DSL-G664T

Linksys BEFSR41V4/BESR41

Linksys Wireless-b

Netgear DG632

Netgear DG834G

Netgear MR814

Netgear Rangemax 802.11n WPN824

Netgear WGT524

SpeedStream 5660 in Router/NAPT configuration. Latest firmware is 2.(3).7. Possible Solution:
o Switch to bridged mode. (For security, firewall your network.)
o When it dies, just power-cycle the router and continue on.

W-Linx MB401-S (and SMC Barricade 7004 BR, which is identical in construction)

WRT54G/GL/GS

Zyxel Prestige 660hw

Possible Solutions:

Open BitComet → options → preferences–>Connection → disable upnp mapping (XP only) AND in Maximum connections per task (limit this number to something below 180 connections, the lower the better)

If problem persists after UPNP mapping is disabled, use Manual PortForwarding Click here

Further issues, Limit your Maximum Connections per task to 50-100.

If all else fails, check if your router is bricked (i.e. Dead Router then, Head here

Otherwise, buy a new router (Do not buy the ones listed in above).

Known Portforwarding issues with Router(s)

Zyxel Prestige 660hw

*Sourced from Azureus’ Bad Routers *

16

My Norton Antivirus continually prompts me to “Permit” or allow BitComet to access the internet & network. But each time I click Permit, a new window pops up again.

Solution

Open your Norton Antivirus

Click Internet Worm Protection on your left tab.

Next, click Program Control on your right tab.

Locate/browse for BitComet, and delete

Click the add button on the bottom

Browse for BitComet’s .exe file (By default C:/Program Files/BitComet/ )

In the next box, click menu (Drop down) → Permit

Click ok.

Re-open BitComet, Norton Antivirus should pop up a new window again asking you to permit/decline BitComet. Click Permit. No new windows should now pop up.

17

BitComet uses 90% or more of my CPU processes, and I’m also using an Nvidia Firewall. What should I do?

** Solution**

If BitComet appears to be using alot of your PC’s memory (or even gradually using alot of your PC’s memory), you must uninstall Nvidia’s firewall. Disabling the firewall will be of no use, as it continues running in the background (i.e. in Processes).

This issue is not inflicted by BitComet, it is Nvidia’s firewall that is causing the problem.

Sources http://forums.nvidia.com/lofiversion/index.php?t2682.html

18

What is DHT? BitComet states that “DHT is not Connected” - What should I do?

Solution

*What is DHT? *

Click Here

Many users are confused as to whether DHT is a tracker of some sort. But in fact, DHT acts almost as a trackerless back-up support which taps into a ‘node’. DHT exploits the possiblities of locating and connecting to BitComet DHT users who may have the torrent file you’re downloading.

As BitComet was one of the first torrent clients to introduce DHT technology into the bittorrent community, we have suffered minor drawbacks, however since 0.62 versions, the DHT issue has been rectified, and now abides by Private Community trackers. Utorrent also utilises our DHT technology.

How can I enable DHT?

Caption: The Green circled area is where the enabling/disabling of the DHT Network can be chosen. On the bottom right hand corner of the client, you should see the status of your client’s DHT Network (i.e. Whether it is connected or not)

All of our latest BitComet releases are enabled by default and can be enabled/disabled in Options → Advanced → Connection → Enable DHT Network.

DHT Connection Status:

A Green Circle at the bottom right hand corner of the client followed by a statement “DHT Connected Node: XXX” means that you’re successfully tapped into the DHT Network.
A Grey Circle at the bottom right hand corner of the client followed by a statement “DHT not Connected” means that you’re not tapped into the DHT Network.
Even if you have NO torrents running (i.e. active), BitComet should automatically connect to it’s nearest DHT Node.

How come BitComet states that my DHT is not connected? What should I do then?

Unfortunately DHT Technology is still in it’s infant stages, and we’re still developing a more efficient coding for it. However, possible solutions to this issue are as follows:

Solution Type 1:

Open BitComet, click Options → Advanced → Connection → UNCLICK Enable DHT Network → Click OK
Close BitComet to allow saved changes to take place.
Reboot PC if possible.
Open BitComet, click Options → Advanced → Connection → CLICK Enable DHT Network → Click OK
Look at the status of the DHT network at the bottom right hand corner.

If Type 1 does not solve your problem, proceed to Solution Type 2.

Solution Type 2:

A: If you use a router, follow the steps below. If you do not use a router, proceed to B

Open your Router Webpage (i.e. 192.168.2.2)
Open the Router Page which controls all the forwarding of Ports. How do I get to my Router’s Portforward Page?

Next, create a new rule, for a UDP Virtual Server type entry. (In other words, in addition to the TCP Portforwarding done for BitComet, you will need to create an EXACT replica of that rule, except it isn’t TCP, but UDP)
Ensure that the UDP Port is exactly the same as your TCP Port. (TCP & UDP Ports should be exactly identical to BitComet’s Listening Port.

Continue on to B if you use a Firewall in addition to your Router

B: If you use a software firewall, follow the steps below:

Open your firewall’s Program Configuration/Control. This is where your firewall controls which applications are allowed to access your network and/or internet.
Locate BitComet.exe ( By default: C: Program Files/Bitcomet/bitcomet.exe )
Add it into your firewall’s exception rule. Also, if your firewall also controls the ‘ports’ used by a program, locate UDP type.
Add in exactly the same port used as in your listening port. (Once again, this should also be the same as your TCP Port).
Make sure your firewall rule updates for use with new versions when you update BitComet. Better firewalls such as McAfee do this automatically.

For Windows Firewall only users:

People who use Windows XP SP-2 firewall need to make sure exceptions are allowed.
BitComet will add the ports for you when the following setting “Enable NAT/Firewall Configuration in ICS/ICF (XP only)” is turned on in Preferences > Advanced > Connections.
Windows Vista users need to the above rule turned on as well as the “Remove Port on NAT/Firewall (XP only)” rule located two settings below.

If after all of this, and your issue still remains. I would suggest you to either try out BitComet 0.64 or, use our latest BitComet Beta Releases

19

How come I see .bc! next to my file(s) within the torrent’s allocated download directory?

.bc! is an added feature by BitComet to notify users that this file is partially downloaded.

How do I turn this feature off?

Options → Preferences → Task → Unclick "Add .bc! file extension for incomplete file.

20

This looks like the best place to talk about what DHT is and how it works. In order to keep it simple, let’s use the example of a telephone directory. That should be familar to almost everybody Here’s part of our directory:

Azureus, Adrian

123 Minor St, Pougkeepsie, IL 54321

101-202-3456

Bitcomet, Bob

27 TCP Highway #404, Chitling Switch, TX 65432

555-666-7777

Utorrent, Uther

P.O. Box 155, Aberrent, AZ 88888

999-876-5432

And so forth. If it’s a printed directory, it’s something everyone has seen and used. Let’s make it a database instead. Now it’s one or more tables (lists, basically) of data in a computer server. The advantage of a database is that we can give it commands like “show me everybody who lives in Arizona”, or “I’ve added some people to the list, so re-sort it”

Now think big. Lots of data about lots of people. Spouse’s name, kids’ names, pet’s name, family doctor, shoe sizes, and many other things. For a whole LOT of people.

A database would be the only sane way to manage such a large list. But if you’re going to do that, you usually need a honkin’ big, powerful and expensive computer to run that database on. You also want it to have all sorts of protective, redundant and backup features so you don’t ever lose the list and it’s always available.

But there is an alternative. Instead of one huge, powerful computer, let’s spread this same list over a whole bunch of small, average computers. The way we’ll do that is to make a code based onf each entry.

We’ll take one entry and use a mathematical function to create a very long unique number out of it. This is called a “hash”. Then we’ll assemble all of these hashes into a single table, along with the records they point to. This is our “Hash table”.

Now we’ll cut the table into small pieces, and give every computer on our network a part of the table. So now it’s a Distributed Hash Table, or DHT.

If you want to look someone up, you take the information you’ve got, such as the name, and compute the hash for that. Then you go into the network and look for the node that handles hashes of that particular range, find the one computer that has that particular entry, and retrieve the information from it.

How do you find that particular node? You ask your neighbors. (You’re in the network too, so you’ve got a small chunk of the table that you’re responsible for too.) You ask another known node (which you discovered when you joined the network), and he points you to another node, which points you to another, and so on until you get to what you’re looking for.

Suppose your part of the table is all the people whose last name begins with “T”. You’re looking for somebody whose last name begins with “H”. Since you yourself are “T”, you know who’s got “S” and who’s got “U”, because they’re your neighbors in this network. If you’ve got some idea of structure, you’ll go towards U, which will point you to V, who will point you to W, then X, Y, Z, A, B, C and so on till you get to the “H” you’re looking for.

If you don’t know the structure, you could go in the other direction, but you try to chose the most efficient if you can. But hashes are numbers (admittedly very LARGE numbers), and you can see how this is easier with numbers.

Instead of addresses and other phone-book information, we’re looking for bittorrent peers. The hash we’re searching for is that of the torrent we’re trying to download. When we locate the correct node, we can get from it a list of all the other peers who are transferring this torrent and who are in the DHT network. We can compare that list to the list of peers that we got from the tracker (if we’ve got one), eliminate any duplicates, and add into our peer list any that are left over. Poof, we’ve got more peers! And we did it without the tracker.

Now DHT goes to sleep for 20 minutes, then it wakes up and queries again, to see if any more peers have joined. If they have, they get added, otherwise it’s back to sleep again.

This whole thing is the guts of a “distributed database”, which is a cool concept. Much more difficult to do than to describe, of course, and there are terrible reliablility/availability problems, but they’re being worked out. The detailed scheme that BitComet uses is based on a scheme called “Kademlia”, which was invented by a couple of grad students. This is a subset of it.

Now since this thing does not talk to the tracker, and doesn’t transfer torrent data, you can fit it right into the existing bittorrent structure without changing that structure at all. This is called an “overlay”. DHT can be added to a bittorrent client and it will still work just fine with other clients that don’t have DHT, because nothing has changed in the structure of communication. Those other clients simply wont’ be part of the DHT network, or even aware of its existence. They also won’t, naturally, be found by that network because they’re not part of it. These clients have to be found via the tracker. The only point of contact between DHT and bittorrent is when additional peers get added into the connection pool, and that happens internally to the client.

In this particular instance, all of the DHT messages we need to send and receive do not require two-way communication. They are like monologues, not conversations. That means that we can use the UDP protocol, which is older and simpler than TCP protocol and doesn’t require the overhead of two-way communication.We can set that right down onto our existing listen port, and since it’s a different protocol, they won’t interfere with each other. The only catch is that we have to open the listen port for UDP in addition to opening it for TCP traffic. Fortunately, that’s very simple to do.

Torrents can optionally disable DHT for the particular torrent. Private torrent sites want you to do that in order to keep their torrents private. However, it is the torrent, at the time it’s created, that controls this. All that the tracker can do is refuse to accept torrents which haven’t disabled DHT. It can’t change them, because you can’t change a torrent after creation. (That means you also can’t add a virus to it, so that’s a good thing.) If you change a torrent, the hashes won’t match any more, and the whole chain will break down.

You can see from all this that DHT is a nice extra, and someday will be used for completely trackerless torrents that can be distributed from, say, your weblog, without needing to set up a tracker. That’s really what it was created for. But you can also see that you don’t NEED to have DHT for normal tracked torrents, and you’ll probably get plenty of peers even without DHT.