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Transcript of Networks
Peer-to-peer networking involves data transfer from one user to another without using an intermediate server.
A peer-to-peer network is designed around the notion of equal peer nodes simultaneously functioning as both "clients" and "servers" to the other nodes on the network.
In structured peer-to-peer networks the overlay is organized into a specific topology, and the protocol ensures that any node can efficiently search the network for a file/resource, even if the resource is extremely rare.
The most common type of structured P2P networks implement a distributed hash table (DHT), in which a variant of hashing is used to assign ownership of each file to a particular peer. This enables peers to search for resources on the network using a hash table: that is, (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key.
While P2P networks use multicast or broadcast, depending of the structure, usually DNS servers use unicast or, like Google's or 12 of the 13 root name servers, anycast.
DHT is widely used in P2P networks, such as BitTorrent, the Kad network, the Storm botnet and YaCy.
DHT-based networks have also been widely utilized for an efficient resource discovery for grid computing systems, as it aids in resource management and scheduling of applications.
In order to route traffic efficiently through the network, nodes must maintain lists of neighbors that satisfy specific criteria. This makes them less robust in networks with a high rate of churn. There are other issues in DHT-based solutions, such as high cost of advertising/discovering resources and static and dynamic load imbalance.
DHT only direct supports exact-match search (key, value) and it is impossible to do keyword search. Due to that, many servers were born to give the possibility of search a content even if you know only its name and not the key.
Each of Google's DNS around the world (with anycast) has many subnets that send requests to root name servers.