Direct Connect (protocol)

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Direct Connect (DC) is a peer-to-peer file sharing protocol. Direct Connect clients connect to a central hub and can download files directly from one another. Advanced Direct Connect can be considered a successor protocol.

Hubs feature a list of clients or users connected to them. Users can search for files and download them from other clients, as well as chat with other users.


NeoModus was started as a company funded by the adware "Direct Connect" by Jonathan Hess in November, 1999 while he was in high school.[1]

The first third-party client was called "DClite", which never fully supported the file sharing aspects of the protocol. Hess released a new version of Direct Connect, requiring a simple encryption key to initiate a connection, locking out third-party clients. The encryption key was cracked, and the author of DClite released a new version of DClite compatible with the new software from NeoModus. Some time after, DClite was rewritten as Open Direct Connect with the purpose of having an MDI user interface and using plug-ins for file sharing protocols (similar to MLDonkey). Open Direct Connect also did not have complete support for the full file sharing aspects of the protocol, but a port to Java, however, did. Later on, other clients such as DCTC (Direct Connect Text Client) and DC++ became popular.

The DCDev archive[2] contains discussions of protocol changes for development of DC in the years 2003-2005.


The Direct Connect protocol is a text-based computer protocol, in which commands and their information are sent in clear text, without encryption in original NeoModus software (encryption is available as a protocol extension). As clients connect to a central source of distribution (the hub) of information, the hub requires a substantial amount of upload bandwidth available.[3]

There is no official specification of the protocol, meaning that every client and hub (besides the original NeoModus client and hub) has been forced to reverse engineer the information. As such, any protocol specification this article may reference is likely inaccurate and/or incomplete.[4]

The client-server (as well as client-client, where one client acts as "server") aspect of the protocol stipulates that the server respond first when a connection is being made. For example, when a client connects to a hub's socket, the hub is first to respond to the client.

The protocol lacks a specified default character encoding for clients or hubs. The original client and hub use ASCII encoding instead of that of the Operating system. This allows migration to UTF-8 encoding in newer software.

Port 411 is the default port for hubs, and 412 for client-to-client connections. If either of these ports are already in use, the port number is incremented until the number of a free port is found for use. For example, if 411, 412 and 413 are in use, then port 414 will be used.

Hub addresses are in the following form: dchub://[:411], where 411 is an optional port.

There is no global identification scheme; instead, users are identified with their nickname on a hub-to-hub basis.

An incoming request for a client-client connection cannot be linked with an actual connection.[5]

A search result cannot be linked with a particular search.[6]

The ability to kick or move (redirect) a user to another hub is supported by the protocol. If a user is kicked, the hub is not required to give that user a specific reason, and there is no restriction on where a user can be redirected to. However, if another client in power instructs the hub to kick, that client may send out a notification message before doing so. Redirecting a user must be accompanied by a reason. There is no HTTP referer equivalent.

Hubs may send out user commands to clients. These commands are only raw protocol commands and are used mostly for making a particular task simpler. For example, the hub cannot send a user command that will trigger the default browser to visit a website. It can, however, add the command "+rules" (where '+' indicates to the hub that it's a command - this may vary) to display the hub's rules.

The peer-to-peer part of the protocol is based on a concept of "slots" (similar to number of open positions for a job). These slots denote the number of people that are allowed to download from a user at any given time and are controlled by the client.

In client-to-client connections, the parties generate a random number to see who should be allowed to download first, and the client with the greater number wins.

Transporting downloads and connecting to the hub requires TCP, while active searches use UDP.

There are two kinds of modes a user can be in: either "active" or "passive" mode. Clients using active mode can download from anyone else on the network, while clients using passive mode users can only download from active users. In NeoModus Direct Connect, passive mode users receive other passive mode users' search results, but the user will not be able to download anything. In DC++, users will not receive those search results. In NeoModus Direct Connect, all users will be sent at most five search results per query. If a user has searched, DC++ will respond with ten search results when the user is in active mode and five when the user is in passive mode. Passive clients will be sent search results through the hub, while active clients will receive the results directly.

Protocol delimiters are '$', '|' and ' ' (  (space)). Protocol have for them (and few others) escape sequence and most software use them correctly in login (Lock to Key) sequence. For some reason that escape sequence was ignored by DC++ developers and they use HTML equivalent if these characters are to be viewed by the user.

Continued interest exists in features such as ratings and language packs. However, the authors of DC++ have been actively working on a complete replacement of the Direct Connect protocol called Advanced Direct Connect.

One example of an added feature to the protocol, in comparison with the original protocol, is the broadcasting of Tiger-Tree Hashing of shared files (TTH). The advantages of this include verifying that a file is downloaded correctly, and the ability to find files independently of their names.

Hub software[edit]

Direct Connect hubs are central servers to which clients connect, thus the networks are not as decentralized as Gnutella or FastTrack. Hubs provide information about the clients, as well as file-searching and chat capabilities. File transfers are done directly between clients, in true peer-to-peer fashion.

Hubs often have special areas of interest. Many have requirements on the total size of the files that their members share (share size), and restrictions on the content and quality of shares. A hub can have any arbitrary rule. Hubs can allow users to register and provide user authentication. The authentication is also in clear text. The hub may choose certain individuals as operators (similar to IRC operators) to enforce said rules if the hub itself cannot.

While not directly supported by the protocol, hub linking software exists. The software allow multiple hubs to be connected, allowing users to share and/or chat with people on the other linked hubs. Direct connect hubs have difficulty scaling, due to the broadcast-centricity of the protocol.


NMDC[7] hub FOSS Software license Active Latest version (release date) GUI
IPv6 support Programming language Based on Notes
UFOHub No Proprietary
Yes 8.16.12 (2016-Nov-27) Yes Yes Yes Yes Unknown
PTDCH Yes GNU GPL Yes Never released since 2008 Yes Unknown Unknown No Visual Basic, Jscript, VBscript DDCH
Dtella Yes GNU GPL Yes 1.2.9 (2015-06-07)[8] No No Yes No Python
HeXHub Yes Open Software License Yes 5.07 (2011-05-29) Yes Unknown Unknown No Assembly
Open Direct Connect Hub Yes GNU GPL No 0.8.3 (2014-08-14) No Unknown Unknown No C, Perl Available in Debian[9] and OpenWrt[10]
Flexhub Yes GNU AGPL Yes Beta0.2svn1469 (2013-10-22) Pending Yes Unknown No Lua
PtokaX Yes GNU GPL Yes (2015-08-16)[11] Yes Yes Unknown Yes C++, Lua
RusHub Yes GNU GPL Yes 2.3.10 (2012-06-10)[12] No Yes Unknown Yes C++, Lua Verlihub[13]
VerliHub Yes GNU GPL Yes 1.0.0-RC4 (2015-02-28) No Yes Unknown No C++, Lua, Python, Perl
Eximius[14] No Proprietary
Yes 2007 Yes Unknown Unknown No C#, Lua
DB Hub Yes GNU GPL No 2008 Unknown Unknown Unknown No Unknown OpenDCHub
openDCd Yes GNU GPL No 2002 Unknown Unknown Unknown No Unknown
DDCH DevDirect Connect Hub Unknown Unknown No Yes No No No Visual Basic, Jscript
py-dchub Yes MIT License No 0.2.4 (2006-02-13) Unknown Unknown Unknown No Python
Aquila Yes GNU GPL No 2012 No Yes No No C++, Lua
YnHub No Proprietary
Yes 1.0363 (2014-02-20) Yes No No No Delphi
LamaHub Yes GNU GPL No (2010-04-25) Unknown Unknown Unknown No C
DC Sharp Hub Yes GNU GPL No 3.0.4 beta (2004-09-06) Unknown Unknown Unknown No C#
NMDC hub FOSS Software license Active Latest version (release date) GUI
IPv6 support Programming language Based on

Operating system support[edit]

NMDC hub Windows
Mac OS X
UFOHub Yes No No No
Eximius Yes No No No
PTDCH Yes No No No
Aquila Yes Yes No No
Dtella Yes Yes Yes No
HeXHub Yes No No No
Open Direct Connect Hub No Yes No OpenWrt
Flexhub Yes Yes No Qnap and Synology NAS Devices
openDCd Yes Yes No No
DDCH DevDirect Connect Hub Yes No No No
DBHub No Yes No No
PtokaX Yes Yes Yes FreeBSD, OpenBSD, NetBSD, Solaris, illumos, Haiku
py-dchub Yes Yes Yes Any Python compatible platform
RusHub Yes Yes Yes FreeBSD, Solaris
VerliHub No Yes No No
Yhub Yes No No No
Ynhub Yes No No No
LamaHub Yes Yes Yes OS/2, OpenBSD, NetBSD, TrueOS, FreeBSD, ZeX/OS, Android[15]
DC Sharp Hub Yes No No No
NMDC hub Windows
Mac OS X

Client software[edit]

For additional clients that are NMDC[16] compatible see ADC Compatible Clients since this list is for NMDC clients only.

While not mandated by the protocol, most clients send a "tag". This is part of the client's description and display information ranging from client name and version to number of total available slots to if the user is using a proxy server. It was originally added to DC++, due to its ability to be in multiple hubs with the same instance. The information is arbitrary. The original client's file list (a comprehensive list of the files a user shares) was compressed using Huffman's compression algorithm. Newer clients (among them DC++) serve an XML-based list, compressed with bzip2.


NMDC Client FOSS Software license Active Windows Linux Mac OS X Other OS GUI CLI Other UI Programming language Based on
MLDonkey Yes GNU GPL Yes Yes Yes Yes No Yes Yes WebUI OCaml, C, assembly
Shareaza Yes GNU GPL Yes Yes No No No Yes Unknown Unknown C++
NeoModus Direct Connect No Proprietary
No Yes Yes No No Yes No No Visual Basic, C++
ShakesPeer Yes GNU GPL No No No Yes No Yes No No C
Valknut Yes GNU GPL No No Yes No FreeBSD Yes No No C++
DCTC Yes GNU GPL No No No Yes C++
DC# Yes GNU GPL No Yes No No No Yes No No C#
LDCC Unknown Unknown No No Yes No No No No Yes C
DCDM++ Yes GNU GPL No Yes No No No Yes No No C++ DC++
fulDC Yes GNU GPL No Yes No No No Yes No No C++ DC++
RevConnect Yes GNU GPL No Yes No No No Yes No No C++ DC++
CzDC Yes GNU GPL Yes Yes No No No Yes No No C++ DC++
EiskaltDC Yes GNU GPL No No Yes Yes FreeBSD Yes No No C++ Valknut
ncdc Yes MIT Licence Yes No Yes Yes FreeBSD No Yes No C
NMDC Client FOSS Software license Active Windows Linux Mac OS X Other OS GUI CLI Other UI Programming language Based on

Other software[edit]

Hub linking software links hubs' main chat, so that users can see and respond to chat that is in a hub they're not directly connected to. Often used to draw in users to hubs, or make private or small hubs more widely known. Whereas advertising a hub is "frowned upon" and is usually repercussion with floods or denial of service attacks, forming a more or less formal network by means of linking hub chat is a legitimate means for getting free publicity. Some Hub programs are able to support a more advanced form of linking which includes all the normal functions, chat, private messages, search and file transfers between users on different hubs can be supported through hub specific solutions or hub software neutral extensions using scripts/plug-ins.


Other software Software type FOSS Software license Active
jDCBot General library Yes GNU GPL Yes
Net::DirectConnect General library Yes Unknown Yes
FlowLib General library Yes GNU GPL Yes
DC-hublink Link Yes GNU GPL No
Hub-Link Link Yes GNU GPL No
MyIrcDcLinks Link Yes GNU GPL Yes
NetChatLink Link Yes GNU GPL Yes
Kitty Bot Yes GNU GPL No
Other software Software type FOSS Software license Active

Operating system support[edit]

Other software Windows
Mac OS X
jDCBot Yes Yes Yes Any Java compatible platform
Net::DirectConnect Yes Yes Yes Any Perl compatible platform
FlowLib Yes Yes Yes Any C# compatible platform
DC-hublink Yes No No No
Hub-Link Yes No No No
MyIrcDcLinks Yes No No No
NetChatLink Yes No No Runs under WINE
Kitty Yes No No No
Other software Windows
Mac OS X

Interface and programming[edit]

Other software GUI
Programming language
Based on
jDCbot No No No Java
Net::DirectConnect No No No Perl
FlowLib No No No C#
DC-hublink Yes No No Visual Basic
Hub-Link Yes No No Visual Basic
MyIrcDcLinks Yes No No Delphi
NetChatLink Yes No No Delphi
Kitty Unknown Unknown Unknown C#
Other software GUI
Programming language
Based on


CTM Detection
Active Yes No Regserver Yes Yes Yes Yes Webbased Yes Yes Yes Yes Webbased Unknown Yes Yes No Unknown Unknown Yes Yes Yes Webbased Yes Yes

Direct Connect used for DDoS attacks[edit]

As the protocol allows hubs to redirect users to other hubs, malicious hubs have redirected users to places other than real Direct Connect hubs, effectively causing a Distributed Denial of Service attack. The hubs may alter the IP in client to client connections, pointing to a potential victim.[17][18][19]

The CTM Exploit surfaced in 2006–2007, during which period the whole Direct Connect network suffered from DDoS attacks.[citation needed] The situation prompted developers to take security issues more seriously.[citation needed]

As of February 2009,[20][21] [22][23][24] an extension for clients was proposed in order for the attacked party to find out the hub sending the connecting users.

Direct Connect Network Foundation[edit]

The Direct Connect Network Foundation (DCNF) is a non-profit organization registered in Sweden that aims to improve the DC network by improving software, protocols and other services in the network.[25]

Articles and papers[edit]

The DCNF maintains a list of articles, papers and more documentation that relate to DC.[26]

See also[edit]


  1. ^ Annalee Newitz (July 2001). "Sharing the Data". Metro, Silicon Valley's Weekly Newspaper. Metro Publishing Inc. Retrieved 2006-10-16. 
  2. ^ [1][dead link]
  3. ^ Fredrik Ullner (April 2007). "Command and bandwidth estimations in NMDC". DC++: Just These Guys, Ya Know?. Retrieved 2007-07-27. 
  4. ^ "NMDC Protocol". Retrieved 2016-12-04. 
  5. ^ "CTM tokens in ADC (or why the NMDC protocol is terrible, part 2)". DC++: Just These Guys, Ya Know?. August 2007. Retrieved 2007-10-07. 
  6. ^ Todd Pederzani (June 2006). "Filtering Redux". DC++: Just These Guys, Ya Know?. Retrieved 2007-08-31. 
  7. ^ NMDC : NeoModus Direct Connect
  8. ^
  9. ^
  10. ^
  11. ^
  12. ^
  13. ^
  14. ^
  15. ^
  16. ^ NMDC : NeoModus Direct Connect
  17. ^ Paul Sop (May 2007). "Prolexic Distributed Denial of Service Attack Alert". Prolexic Technologies Inc. Prolexic Technologies Inc. Archived from the original on 2007-08-03. Retrieved 2007-08-22. 
  18. ^ Robert Lemos (May 2007). "Peer-to-peer networks co-opted for DOS attacks". SecurityFocus. Retrieved 2007-08-22. 
  19. ^ Fredrik Ullner (May 2007). "Denying distributed attacks". DC++: Just These Guys, Ya Know?. Retrieved 2007-08-22. 
  20. ^ Jan Vidar Krey (February 2009). "Referral extension". DC++ Launchpad Page. Retrieved 2009-02-11. 
  21. ^ Jan Vidar Krey (February 2009). "Referral extension on ADCPortal wiki". Retrieved 2009-02-11. 
  22. ^ Eugen Hristev (February 2009). "DC++ pointing out the corrupted". DC++: Just These Guys, Ya Know?. Retrieved 2009-02-11. 
  23. ^ Toast (January 2009). "CTM Review and the errors of past". ADCPortal. Retrieved 2009-01-27. 
  24. ^ Fredrik Ullner (July 2011). "Long lost response regarding DC being used as a DDoS tool". DC++: Just These Guys, Ya Know?. Retrieved 2011-07-20. 
  25. ^ [2][dead link]
  26. ^ [3][dead link]

External links[edit]