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- ---
- order: 1
- parent:
- title: Consensus
- order: 6
- ---
-
- # Consensus
-
- Tendermint Consensus is a distributed protocol executed by validator processes to agree on
- the next block to be added to the Tendermint blockchain. The protocol proceeds in rounds, where
- each round is a try to reach agreement on the next block. A round starts by having a dedicated
- process (called proposer) suggesting to other processes what should be the next block with
- the `ProposalMessage`.
- The processes respond by voting for a block with `VoteMessage` (there are two kinds of vote
- messages, prevote and precommit votes). Note that a proposal message is just a suggestion what the
- next block should be; a validator might vote with a `VoteMessage` for a different block. If in some
- round, enough number of processes vote for the same block, then this block is committed and later
- added to the blockchain. `ProposalMessage` and `VoteMessage` are signed by the private key of the
- validator. The internals of the protocol and how it ensures safety and liveness properties are
- explained in a forthcoming document.
-
- For efficiency reasons, validators in Tendermint consensus protocol do not agree directly on the
- block as the block size is big, i.e., they don't embed the block inside `Proposal` and
- `VoteMessage`. Instead, they reach agreement on the `BlockID` (see `BlockID` definition in
- [Blockchain](https://github.com/tendermint/spec/blob/master/spec/core/data_structures.md#blockid) section)
- that uniquely identifies each block. The block itself is
- disseminated to validator processes using peer-to-peer gossiping protocol. It starts by having a
- proposer first splitting a block into a number of block parts, that are then gossiped between
- processes using `BlockPartMessage`.
-
- Validators in Tendermint communicate by peer-to-peer gossiping protocol. Each validator is connected
- only to a subset of processes called peers. By the gossiping protocol, a validator send to its peers
- all needed information (`ProposalMessage`, `VoteMessage` and `BlockPartMessage`) so they can
- reach agreement on some block, and also obtain the content of the chosen block (block parts). As
- part of the gossiping protocol, processes also send auxiliary messages that inform peers about the
- executed steps of the core consensus algorithm (`NewRoundStepMessage` and `NewValidBlockMessage`), and
- also messages that inform peers what votes the process has seen (`HasVoteMessage`,
- `VoteSetMaj23Message` and `VoteSetBitsMessage`). These messages are then used in the gossiping
- protocol to determine what messages a process should send to its peers.
-
- We now describe the content of each message exchanged during Tendermint consensus protocol.
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