A DHT (Distributed Hash Table) is a Hash Table that is distributed. That being said it is much more complex than that. The routing portion is the hardest part. There are 2 major variants of DHTs out there.

1.) Chord

Chord works in a circle based system so there is a limit to the amount of nodes in the dht. The DHT is for systems that are private and want more of a graceful close to pass data to the other nodes before the leave. When it tries to find a file or data it searches the file or data hash on other nodes the node with the closest XOR ID to the file or data hash.

• Typically is TCP.

https://github.com/DrBrad/JChord

https://en.wikipedia.org/wiki/Chord_(peer-to-peer)

Commands:

• JOIN - Join network use ID to find place
• LEAVE - Tell neighbors your leaving
• PUT - Give file or data to node closest to id of data and neighbor
• FIND - Get node closest to file then returns file or data

2.) Kademlia

Kademlia works on an XOR bucket based system. Each node assigns itself an ID based off of IP or something with SHA1 or CRC32c. It then uses this when a part of the network. When it tries to find a file or data it searches the file or data hash on other nodes the node with the closest XOR ID to the file or data hash.

• Typically is UDP.

https://github.com/DrBrad/Kad4

https://github.com/DrBrad/Kad4/wiki

Commands:

• PING - Check if node it alive
• FIND_NODE - find node closest to XOR of given query ID
• PUT - put file or data to 5 nodes closest XOR to ID based off of hash
• GET - get file or data closest to hash of file based off of ID XOR.

Basic jist is file or data closest based off of a hash should be stored on node closest to it.