Structure:

• Each node in the network is assigned an ID using a hash function
• This unique identifier is used to determine the node's position in the DHT
• DHT uses key-value pairs. The key is a hash used to find the value in the DHT
• Routing Table: Each node maintains a routing table about the network.
  • Helps nodes efficiently locate other nodes nd the data they store.
  • Includes a list of known nodes and their IDs
  • Includes info about the distance to these nodes

Data storage:

• A node wants to store a key-value pair
• It hashes the key to find the node responsible for it
• The data is then sent to that node for storage.

Lookup Process:

• A node wants to retrieve a value from a key
• It hashes the key to find the responsible node
• Routing table is used to navigate the network
• Queries nodes along the way until the target node is reached

Nodes Joining:

• A new node joins the network
• It finds existing nodes and updates its routing table
• Existing nodes are found via a bootstrapping mechanism
• It then claims a portion of the keyspace (range of keys it will manage)

Bootstrapping mechanisms:

• Hardcoded Bootstrap Nodes, i.e. nodes that are known to be always online
• DNS Seeders, i.e. domain names that resolve to IPs of known nodes
• Peer Discovery Protocols, i.e. allowing nodes to advertise their presence
• Previous Connections: memory of previous connection can be used to find a node
• Public Nodes: Nodes that are advertised on forums, websites, etc.

Nodes Leaving:

• When a node leaves, its data must be redistributed
• It transfers data to its successor or other nodes
• If the node leaves without doing this, it's a failed node

Replication and Fault Tolerance:

• Data replication is often implemented
• Copies of data are stored on multiple nodes.

Consistency and Maintenance:

• Mechanisms needed to maintain consistency and handle changes in the network
• Can involve periodic updates to routing tables and data rebalancing

DHTs are used in

• peer-to-peer file sharing
• decentralized storage systems
• blockchain networks

Popular DHT implementations include

• Kademlia
• Chord
• Pastry