Network Layers

The Lightning Network is an overlay network on top of another blockchain. To avoid confusion it is crucial to differentiate between the following network layers we encounter when reasoning about lnd:

• Bitcoin Network: This is the underlying blockchain that lnd rests on top of. lnd needs a way to communicate with the underlying blockchain in order to send on-chain payments, create channel open/close transactions, and watch for events on the blockchain.

• P2P Network: This is the peer layer where lnd nodes add each other as peers so they can send messages between one another via an encrypted connection. For example, the lncli connect adds a peer, which are identified by identity pubkey and IP address.

• Payment channel network: This is the layer where nodes are connected by payment channels. For example, the lncli openchannel command opens a channel with a node that was already connected at the peer layer, and the lncli describegraph command returns the list of edges and vertices of the payment channel graph.

Software Components

There are distinct software components we should be aware of when developing on

• ​btcd or bitcoind is used by lnd to interface with the underlying blockchain.

• lnd / lncli: lnd stands for Lightning Network Daemon and serves as the main software component driving the Lightning Network. It manages a database, connects to peers, opens / closes channels, generates payment invoices, sends, forwards, and revokes payments, responds to potential breaches, and more. lncli opens up a command line interface for driving lnd.

• ​Neutrino is an experimental Bitcoin light client designed to support Lightning mobile clients. This is a wallet UI usable with lnd. Neutrino is not required from an application development standpoint, but can be regarded as the primary way for an end-user of lnd to interact with the Bitcoin Network and the applications built on top of it.

LND Interfaces

There are several ways to drive lnd.

• lncli is the lnd command line tool. All commands are executed instantaneously. A full list of commands can be viewed with lncli --help. To see a breakdown of the parameters for a particular command, run lncli <command> --help

• gRPC is the preferred programmatic way to interact with lnd. It includes simple methods that return a response immediately, as well as response-streaming and bidrectional streaming methods. The Beginner's Guide focuses on interacting with the gRPC API via Typescript.

• lnd also features a REST proxy someone can use if they are accustomed to standard RESTful APIs. However, REST does not have full streaming RPC coverage.

All of these lnd interfaces are documented in the API Reference, featuring a description of the parameters, responses, and code examples for Python, Javascript, and command line arguments if those exist.