{{short description, Search method on a peer-to-peer network Query flooding is a method to search for a resource on a peer-to-peer network. It is simple and scales very poorly and thus is rarely used. Early versions of the

Gnutella Gnutella is a peer-to-peer network protocol. Founded in 2000, it was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model. In June 2005, Gnutella's population was 1.81 million computer ...

protocol operated by query flooding; newer versions use more efficient search algorithms.

Operation

A peer-to-peer network generally consists of a large number of nodes each connected to a small subset of the nodes and not all nodes in the network. If a node wants to find a resource on the network, which may be on a node it does not know about, it could simply

broadcast Broadcasting is the data distribution, distribution of sound, audio audiovisual content to dispersed audiences via a electronic medium (communication), mass communications medium, typically one using the electromagnetic spectrum (radio waves), ...

its search query to its immediate neighbours. If the neighbours do not have the resource, it then asks its neighbours to forward the query to their neighbours in turn. This is repeated until the resource is found or all the nodes have been contacted, or perhaps a network-imposed hop limit is reached. Query flooding is simple to implement and is practical for small networks with few requests. It contacts all reachable nodes in the network and so can precisely determine whether a resource can be found in the network (

Hyphanet Hyphanet (until mid-2023: Freenet) is a peer-to-peer platform for censorship-resistant, anonymous communication. It uses a decentralized distributed data store to keep and deliver information, and has a suite of free software for publishing and ...

, for example, only returns a probabilistic result). On the other hand, every request may cause every node to be contacted. Each node might generate a small number of queries; however, each such query floods the network. Thus, a larger network would generate far more traffic per node than a smaller one, making it inherently unscalable. Additionally, because a node can flood the network simply by issuing a request for a nonexistent resource, it could be possible to launch a

denial-of-service attack In computing, a denial-of-service attack (DoS attack) is a cyberattack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host co ...

on the network.

Alternatives

Version 0.6 of the Gnutella protocol mandates ''query routing''. The query routing specification explains how the ideas of the original research are implemented. Other file-sharing networks, such as the

Kad network The Kad network is a peer-to-peer (P2P) network which implements the Kademlia P2P overlay protocol. The majority of users on the Kad Network are also connected to servers on the eDonkey network, and Kad Network clients typically query known node ...

, use

distributed hash table A distributed hash table (DHT) is a Distributed computing, distributed system that provides a lookup service similar to a hash table. Key–value pairs are stored in a DHT, and any participating node (networking), node can efficiently retrieve the ...

s to index files and for keyword searches.

BitTorrent BitTorrent is a Protocol (computing), communication protocol for peer-to-peer file sharing (P2P), which enables users to distribute data and electronic files over the Internet in a Decentralised system, decentralized manner. The protocol is d ...

creates individual

overlay network An overlay network is a logical computer network that is protocol layering, layered on top of a physical network. The concept of overlay networking is distinct from the traditional model of OSI model, OSI layered networks, and almost always assum ...

s for sharing individual files (or archives). Searches are ''performed'' by other mechanisms, such as locating torrent files indexed on a website. A similar mechanism can be used on the Gnutella network with

magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

links. For instance Bitzi provides a web interface to search for magnet links. Earlier P2P networks, such as

Napster Napster was an American proprietary peer-to-peer (P2P) file sharing application primarily associated with digital audio file distribution. Founded by Shawn Fanning and Sean Parker, the platform originally launched on June 1, 1999. Audio shared ...

, used a centralized database to locate files. This does not have a scaling problem, but the central server is a single point of failure.

Operation

Alternatives

See also