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GnuFU: Gnutella For Users

What is Gnutella, and how does it work?

Gnutella ( is an open file sharing Network ( originally created by Justin Frankel of Nullsoft. That means, unlike most other networks, everyone can write a client which can access the GNet, if it fulfills the publicly available specifications. The specifications are discussed and created by the GDF ( (the gnutella development forum), an open Mailinglist for developers, with by this date over 1000 members. After that they are documented in the Gnutella Protocol Specification ( That way all programs share a common base, while the protocol also allows for client specific options. The developers are careful to ensure the greatest possible backwards compatibility.

Despite the name, Gnutella isn't GNU-Software, though some Gnutella clients are GPL-licensed. It is an open network, and the origin of its name may be found more easily by eating too much Nutella, than at GNU (That means: Gnutella is not a project of the FSF or related to GNU software tools).

One sibling of Gnutella deserves special attention, even though some developers of current clients would deny it. It is called MP (Mikes Protocol) or the Shareaza Protocol by most Gnutella developers, while its developer called it Gnutella2, a name which gave his program (Shareaza) much media coverage and created and creates much controvery and aversion against it in the_gdf. More about it here: MikesProtocol.

Back to the main focus of this document: the basic principles of gnutella, their evolution during the last few years (especially the last year) and future plans for it.

Basics of Gnutella

Network model: The Original: FoF

You can imagine the original model of the Gnutella network as friends phoning each other to get information. One asks five others, each of whom asks 5 others and so on. After the first step the number of people reached is 5, after the second it is 25, after the 5th 3125, after the 7th 78,125 and after the 14th about 6.1 billion. That would be enough to reach every human being on this planet. The original Gnutella used 7 steps (called HTL: Hops To Live).

A Problem with this model (among others) is that you have to be a part of the clique before you can use it. There have been several ideas to solve this problem. I will show you three of them.

Getting in: The first way: Pong-Caching

Pong Caching means that the node (aka you) asks its friends who their friends are. It means your friends introduce you to their friends, especially friends whom they value highly, and you write all new adresses in your phone-book, so you know whom to phone when your original friends are on holiday (Somehow like being at a continous cocktail party). It is easy and has the advantage of giving you very reliable contacts, but there is no way of getting into the network without knowing at least one contact who is already in the net. That means you can always get back in, but won't be able to connect if you never did before.

Getting in: The second way: Remember who answers

The second way is really simple. When one of your 5 friends calls back to say Smith (whom you didn't know before) knows something, you note her number. When you call him the next time as one of your five direct contacts, the chance is greater that you will get your information more quickly, because he will likely have friends who have similar interests to you (where else should he have gotten the information?), and those are more likely to have your information than randomly picked persons (at least when you ask about something similar to your last question). The drawback is that those contacts might not be at home often, so it might be that you find a contact with great knowledge, but whom you'll never be able to reach again. Still no way of getting in the first time. And now we get to one of the recent developements in Gnutella: GWebCaches. I will discuss them in the next part.

Recent changes in Gnutella

Getting in: The third way: GWebCaches

To stay within the picture, a GWebCache is a contact who puts her phone number into the newspapers and keeps a record of those who call. When you've been away for some time and are no longer certain if your contacts still have the same mobile-phone numbers, you call the publicly known contact. Before giving you numbers, he/she will ask you: "Do you know other publicly known contacts? If yes, please tell me their numbers." That is done because they can't read all the newspapers, and you do it all the time without working too hard for it. That way, they keep track of each other. Then the contact gives you some numbers to call and notes your number (to give it to someone else) and the adresses of other public contacts he/she knows (GWebCaches).

This is roughly the way GWebCaches work. As I stated, they are one of the new developements in Gnutella, and thus I will now get to some more of the recent changes within Gnutella and to future plans.

Sidenote: GwebCaches are essential only for the first connections, and only when the local host-cache is empty, but they must not be preferred over your local address-book.

Getting in: The fourth way: UDP Host Caching

UDP Host Caching (UHC) works like a mix between Pong-Caching and GWebCaches, but it uses a different way to transport messages: UDP, while Pong Caching and GWebCaches use TCP.

The difference between UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) can be compared to sending an sms instead of making a phone call.

In UDP you don't know, if your info arrived, and to answer or to ask something in return, the receiver has to write a message to you instead of just asking back on the line. But as tradeoff, UDP is a good deal faster, and you don't have to wait till the other side takes up the phone (you might have seen the equivalent to a ringing phone in your Gnutella Client of choice: "Establishing TCP connection" and "Handshake". These mean: The programs negotiate, if they really want to talk to each other, just like you looking on the number of the caller in your mobile phone). The wikipedia offers you additional information about UDP ( and TCP (

Two other things in UHC differ from the Pong-Caching:

  1. In Pong-Caching, a Gnutella program just asks someone to whom it is already connected. In UDP-Host-Caching, now, your program has a seperate list of UDP-Host-Caches, and it always asks those, who are online for the longest amount of time. This is like not asking those of your friends, which you ask for information, whom else they know, but asking someone of whom you know that he/she knows many people, what he/she thinks whom you should call to get your info.
  2. Different from Pong-Caching, a UDP-Host-Cache can also be hosted by a webserver, so it will be online all the time and will always have the same IP (which is similar to keeping the same telephone number).

And different from GWebCaches, the UDP-Host-Caches can also be simple Gnutella Programs, and so Gnutella got rid of having to rely on the GWebCaches, which could be attacked easily (by calling them so often with false calls, that they don't have time to answer important ones)

As a side-note: You program still has Pong-Caching and remembers who answers, and if that information gives you enough numbers of people to call, it won't bother one of the UDP-Host-Caches with a needless question about more numbers which your program wouldn't use anyway.

So UDP-Host-Caching is another way to ensure, that you can always find numbers of people to call, and it makes Gnutella independent of central lists again.

Problems of the FoF-model -> Changes

The Friend-of-a-Friend model has certain disadvantages, which have their source in the way searches are performed. If a search brings too many results, the nodes, through which you are connected (your nearest 5 friends) can get overloaded, because every answer has to go through them, for they don't give out your "phone number", but their own and hand the answer to you. If you ask for the name of the head of University in the campus, you'll get hundreds of answers in reality, and thousands to millions on the web. Also, if every question is passed to every one in a 75,000 to 600,000 computer-network, and every computer asks only once an hour, each of them has to answer about 130 to 1600 questions per second. And they have to pass them on. While computers are fast, and today's internet connections can handle quite a lot when compared to the connections a few years ago, this is too much even for them. Just imagine your phone ringing endlessly the whole day for all kind of questions.

Network model: Change who calls whom: Ultrapeers and Leafs

UPs really short

You'll surely have friends who know very many other people, and whom you can ask, and be sure they'll know exactly the person who can give you the answer. These are called Ultrapeers in Gnutella. An Ultrapeer doesn't have to know much himself/herself, he/she just needs to know who knows it. In Gnutella that means that a good Ultrapeer doesn't need to have many files to benefit the network. If you're afraid to share much, you should become an Ultrapeer in Gnutella.

Ultrapeers and Leafs more detailed

In the Computer World, as in the Real World, there are contacts who can cope with more calls, and those who can't phone often (or can't afford the bills). In the Real World this is because they have more free time. Whereas, in the Computer World, it is because they have faster connections (Like DSL, Cable, T1, T3 or similar broadband). Upon realizing this, the developers decided to change the topologiy, that means how the network looks from the outside when you draw it. Now you don't just call any of your friends, but only those whom you know have the time to take your call and to send it on to others. To save you from too many calls, they then ask you which kinds of informations you have or, to express it in a more human way, what your speciality is. In the Computer World that means your computer sends a list of all its files to the Ultrapeer, which is how we call these kinds of contacts. That list contains summaries (Hash-Strings) of all your shared files (those you decide to let others download) by which the downloader can verify that they are, indeed, the files he or she wants. Whenever a call reaches the Ultrapeer, it checks if you could know an answer and calls you only in that case.

These Ultrapeers have many connections to others, which means they have a really big address book. Normally they stay in contact with 16 other Ultrapeers whom they have in their address book and to whom they send questions, and who send them to 16 more, each. Also they have about 16 leafs (leafnodes), who can't or don't want to phone that much, from which they accept calls, and whose files or, for the human world, specialities they know.

This may seem like a foul bargain for the Ultrapeers, who devote far more resources to keeping the network intact than leafs, but in fact it isn't. While the Ultrapeer (UP) uses much of her time for keeping the network running, the leafs specialize on gathering and delivering information. So, when anyone, Ultrapeer or Leaf, wants to know something, he or she simply starts a call and a leaf specialist can explain it to them. That way people specialize to get more for all.

Besides: The leafs got their name, because they look like leafs on a tree (when you draw the network-structure), while the UPs are the branches.

Network model: Intra-ultrapeer QRP

While with Ultrapeers not everyone needs to participate in sending questions to others, and people can specialize in sharing their information instead, the Ultrapeers would still send every question to everyone, without ever taking into account if that UP even has leaves, who have the files. This sounds normal, for how can an Ultrapeer know which files the other Ultrapeers have? The answer comes, again, from real life. A normal person knows her friends, and knows who of them might know the answer to a specific question, and who most surely will not. In Real Life this is mostly done through friendly chatting.

Now, computers normally don't chat idly, so they don't exchange this information by the way. Thus the Query Routing Protocol was developed. There each Leaf tells its Ultrapeers which files it has, but instead of taking the names, which would consume too much space, each word which is part of the name of a file is saved as numbers (these are computers after all). You can imagine this process like a game of dumping ships (the numbers form the board with two coordinates). An Ultrapeer doesn't send all questions to a leaf, but only those which it might be able to answer (which hit a ship), and so Leafs get far less needless calls.

When this takes so much pressure off the leaves, why not extend it? Exactly that was done. Now all Ultrapeers send their boards to their direct neighbors. They send only those searches, which have one more step to go, to other Ultrapeers on whose board they score a hit. That means, the last two steps of a search will only be taken when there is a chance that they give results. You can see quite simply why this heavily reduces the bandwidth usage: imagine a tree, a normal tree, not one of those mathematical constructs. If you try to count the leaves, you have almost no chance. But if you take the leaves away and count only the branches, you have far less work to do. If you now take away all those tiny branches, you can really begin to count them. QRP doesn't take all leaves and all tiny branches away, but it removes those of them who couldn't give you an answer. Since every part through which a question has to travel consumes bandwidth, and there are far more leaves than branches, taking away, in many cases, many of the last two steps (that means many of the leaves and the tiny branches) reduces the number of questions the computers have to send on (there are far more leaves, than branches). The example doesn't work for all of Gnutella, but here it fits nicely. The people of LimeWire talk about 70-80% savings alone through this.

Network model: Change Searching: Dynamic Querying

Now, while the Ultrapeer model and QRP partly solve the problem that you don't have the time to explain something properly to someone else, or to get it explained, because the phone rings endlessly for questions to which you know no answer (or in Tech-Speech: because the network-traffic exceeds your connection-speed or you just don't have fitting sources), there is still another problem which might normally not even be visible, if you look at it. In the Real World, an Ultrapeer will ask for a specialist who can give you the info until he/she finds one, and then stops. In the Computer-World, the question is sent on and on, to as many contacts as possible, without looking if there already are answers.

With dynamic Querying that changes. Now the Ultrapeers ask one other Ultrapeer at a time, and wait a bit, to see if they get answers. When they have enough answers to be satisfied, they stop asking for more. It sounds pretty natural, but was quite a big step for Gnutella because it saves resources which were wasted on very popular questions. I'll take the example of the of the head of university again: now, if you ask for the head of university, your Ultrapeers will first see if they know someone directly who can answer your question. Then they will simply give you some numbers of people they know who live on the campus. You will still get more than one answer because they will give you more than one number, as they can't be sure that you'll reach every number they gave you. But you won't get thousands of phone-numbers (one from every student on the campus), first because the Ultrapeers would waste their time with that on something which doesn't give you additional benefit, second, because you couldn't ever call all those people, and third, because then you might not reach your Ultrapeers anymore, because they would be too busy getting return calls from others who tell them numbers, and sending your question to other Ultrapeers.

Finding sources without searching aka the Download-Mesh

Now you might say, "but I can't download from those three, because others already do. I want to get all addresses from which I can download," (and you are not alone with this. I feel the same). By looking at the Real World, we can find a solution to this problem too, without having to waste too many resources on it. There (in the Real World), if you ask a specialist to explain something to you, and that specialist is busy, he or she will know some other specialists (because they know each other) who might have more time at the moment.

Getting this into Gnutella is not as easy as the Ultrapeer-Leaf Model nor as the Dynamic-Query Model. But the programmers found a way. As I stated at the Dynamic-Query-Model, you will get more than one number where you can ask. Now, when you call someone who should know the answer, you also give him or her the other numbers you know about. That way, the specialists will get to know each other (the same way, as the GWebCaches, which I mentioned before, learn of others of their kind). As everyone who asks also brings her own set of numbers, the specialists know more and more additional addresses, and when you ask them to explain, and they don't have time at the moment, they give them to you (they do it even if they have time, just in case they could be interrupted, and because in Gnutella you can download from more than one source at once, just like you can in the overnet-network (which does this to the extreme, but is only really efficient for big files)). Additionally, the specialists also add you to their number of alternate-contacts, as soon as you know enough to teach others.

This is why often many people download files from you which you just downloaded yourself.

Better Downloading Part1: Swarming and Partial File Sharing

Swarming is quickly explained (but hard to do in the friend-of-a-friend model, so I drop it for this part only). It works by simply getting one file from more than one person at once. The file is simply separated into several parts, as if you'd want to get a book from some friends and every one of them copied only a few pages of it. When you ask every one of them to copy a different part of the book, you'll get the complete book, and every one of them has only very little work to do (and if one doesn't have the time to do it, another one can).

Swarming works best with the Download Mesh and Partial File Sharing (PFS), which allows people to share files which they are downloading at the moment, because they can share those parts which they already have, while they still download from others. You can copy those pages which you have without having to have the whole book, since your pages are all numbered and friends can ask you for certain page numbers.

Better Downloading Part2: Downloading through Firewalls

Imagine there were people who couldn't be called, but could only call others (maybe because they only use public phones, or their number isn't displayed on your phone, and they don't like to give it out because they don't like being called by telemarketers, or by people terrorizing them over the phone). In Gnutella these are computers who are behind a firewall. They can call others and get information from them, but no one can call them.

The solution is to have the firewalled people call their Ultrapeers regularly and, when someone wants to call them, he or she simply calls the Ultrapeer who then holds two phones together, one to which the firewalled person (the one who can't be called) raised a call, and the one you called. That way you can talk to the firewalled person, but it takes two simultaneously running calls, which means, that it needs twice the bandwidth in the Computer-World. Firewalled persons always keep their connection to the Ultrapeers, who simply relay the information or data.

There are plans to save the Ultrapeers from this additional bandwith usage by letting other people do the phone connecting. Then, when someone wanted to get information from a firewalled specialist, the Ultrapeer would tell the firewalled person and the asker to call a third person. That person would then hold the two phones together. In Gnutella most People have three to five phones, so this wouldn't be such a great problem. These phone-connectors will most likely be called routing-peers.


File-Magnets stray from the Friend of a Friend model. They are links on webpages, which you can simply click, and which will tell your file-sharing program to search Gnutella (in fact also other networks) for a specific file, and to download exactly this.

You can imagine it like an article in a newspaper which tells you information which gives your Ultrapeers the exact information that the specialist, from whom you want to learn, has to know. In the Real World you would most likely find one specialist and those who learned from him or her.

With a magnet-link you can avoid getting bad files because they use a hash-string, which is something like a summary of the information the specialist would give you. If he or she begins to tell you crap, you will see at once that it doesn't fit the summary. In Gnutella, the program asks for files to which the people who have them have assigned the same summary, aka Hash-string. After downloading, the program does its own summary and checks if they really match. If not, it tells you that the file is corrupt. The summaries from same files are always exactly the same because they are done via specific mathematic methods which always get to the same result when given the same data (aka information).

Different from Magnet-Links, KaZaA-Links and eDonkey-Links are not secure, because they use methods which can be betrayed with false files (for example a KaZaA-Link asks for a kind of summary which only checks the introduction and the first part of the information, but all the rest is ignored to make the summary quicker to create. Naturally it is very easy to give you false information, because they only have to tell the truth at the beginning, then they can lie or fantasize as much as they want). Further information on Magnet-Links can be found here: Magnet-Uri ( and on (

There is now a new version of magnet-links: KaZaA magnets. Sadly those aren't secure, for they use the KaZaA hashing system (the incomplete summary) with some changes (they now add another smaller summary, which might tell you about the missing parts, but they didn't publish, how they create it). If KaZaA-Magnets provide information about a search term, they might work with Gnutella, but they won't ensure that you get what they offer to you. If you find the word "kzhash"in the link, it might not be secure (aside from having a somewhat misplaced name).

You'll find some magnet-links on the pages listed on MagnetLists.

What's New: Finding new files in Gnutella

For the case where you don't want to search for a specific file, but simply want to see new files in the network, many Gnutella clients now implement a "What's new" search.

It works by simply asking all your friends to tell you about their newest files.

If you are a leaf, your ultrapeer friends will also tell you about the new files of their leafs, so that you will get a high number of results.

What you should note is, that you see the new files in your neighborhood.

What's New searches are implemented in LimeWire and Phex.

Future Plans

  • Community-Feature
  • Encryption - Making it impossible for the provider to see what you are downloading.
  • Privacy (See AnoGnut )
  • Caching of popular content
  • Magma-Links - Multiple-file-magnets, like playlists.
  • Grouping by language/locale (Implemented in LimeWire, allows you to find documents in your own language far easier)

How to get in?

To become part of the Gnutella Network, you can use one of the clients listed on Gnutella ( (should that be down, just use this list, or the list on: dmoz (, or better still, learn to program and help furthering the development of some of the open-source clients). I'll list some clients here, though this list needn't be exhaustive. If you know a client not listed here, please add it.

Free Clients

  • LimeWire ( A Cross-Platform Java Client, GPL (free software, offers a pro-version with support.
    • FrostWire ( A free spinoff from LimeWire without commecial interests.
  • Phex ( - Another free Cross-Platform Java Client, but with additional configuration options, private network and magma support and without commercial interests.
  • Gtk-Gnutella ( - A GPLed-client for Linux
  • Shareaza ( - A big client for Windows, MultiNetwork (Gnutella, eDonkey, BitTorrent and Gnutella2 aka MikesProtocol)
  • Gnucleus ( - A LGPL Client for Windows COM-based
  • ezpeer ( - A Chinese client. I don't know any more about it, as I don't speak mandarin. I'd be glad if you could send me information at my [ email] in English, German or Esperanto.
  • pp365 ( - Another chinese Client.
  • POCO ( - Jet another chinese Client using GnucDNA.
  • XNap ( - A multinetwork program in Java using the Limewire Core for Gnutella.

Closed Source Clients

  • Acquisition ( - A Mac OS X client based on the limewire core (which is the sole part licensed under GPL in Acquisition), Interface written in cocoa, shareware.
  • Bearshare ( - A big client for Windows >sold to iMesh after legal threats; take care<
  • CocoGnut ( - A commercial client for RISC OS
  • Swapper ( - A free closed source client for Windows utilizing .NET
  • TrustyFiles ( - Another Windows client, which once used GnucDNA and supports FastTrack (KaZaA), Gnutella and G2 aka MikesProtocol,

Links for Users

  • Mac-P2P-FAQ ( - A FAQ on p2p-filesharing MacOSX with the main focus on Acquisition.
  • Zeropaid ( - A p2p-Community, often somewhat rude.
  • Gnutellaforums ( - Forums about Gnutella in General and specific GNet clients.

Resources for Developers

  • the Gnutella Development Forum mailinglist ( - THE source for information about Gnutella and the place to meet other developers.
  • GnucDNA ( - A component for building P2P applications. COM based.
  • Gnucula ( - A project attempting to implement GnucDNA in portable C++, for *nix systems and Mac OSX.
  • open-limewire ( - The Limewire Sourcecode (Java). The core can be used like GnucDNA.
  • LimeWire Source-packages ( - The LimeWire sourcecode displayed as webpages.
  • rfc-gnutella ( - The official specifications of the network-protocol.
  • GNet-Specs ( - Specifications in a wiki, more recent.
  • Gnutella Technical in the LimeWire Wiki ( - A precise description how to write for the Gnutella network.
  • Magnet-Uri ( and ( - Information on Magnet-Links.
  • Infolio Gnutella Developement Directory ( - Interesting papers on Gnutella.
  • GnutellaPapers - A list of academic resources on and about Gnutella

This document is being published under the GFDL, the Gnu Free Documentation license, which you can find here ( Iin its current state it is also avaible under the Creative Commons Attribution-ShareAlike-licence as PDF (

  • Janet did a great Job proof reading and smoothing the text.
Pages using GnuFU
  • Phex-FAQ (

As this page was down two times during the last week, I decided to no longer depend completely on any provider to host this page. Should GnuFU go down due to any reason, a freenet-mirror of the PWP-code can be found using the following key: SSK@1~6U-1UApvA5hld50tMsau3O5tEPAgM,kr~pLjSLxfECXC2Mvt3RKw/gnufu/3//index.html

To access this mirror you need to obtain freenet, a completely decentral and anonymized distribution tool, from .

The follwoing link should normally get you there directly, if you have freenet active: GnuFU_free (,kr~pLjSLxfECXC2Mvt3RKw/gnufu/3//).

Arne Babenhauserheide ( - wrote most of the document. It was opened to the public around the 30th of November 2003. Everything which changed since then belongs to the author of that part, and shall be his or her responsibility (as far as that is possible). I'll still try to keep this structured and easy to read.