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*[Byzantine fault tolerant]: Ability to function correctly and reach consensus despite nodes failing or propagating incorrect information to peers.
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# Comparing Proof of Authority Consensus Protocols
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Pantheon implements the Clique and IBFT 2.0 Proof of Authority consensus protocols. Proof of Authority
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consensus protocols are used when participants are known to each other and there is a level of trust between them.
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For example, in a permissioned consortium network.
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!!! note
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IBFT 2.0 is under development and will be available in v1.0.
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Proof of Authority consensus protocols allow faster block times and have a much greater throughput of transactions
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than the Ethash Proof of Work consensus protocol used on the Ethereum MainNet.
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In Clique and IBFT 2.0, a group of nodes in the network act as signers (Clique) or validators (IBFT 2.0). These nodes propose, validate,
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and add blocks to the blockchain. Nodes are added to or removed from the signer/validator pool by the existing group of nodes voting.
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!!! note
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For the rest of this page, the term validator is used to refer to signers and validators.
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## Properties
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Properties to consider when comparing Clique and IBFT 2.0 are:
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* Immediate finality
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* Liveness
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* Speed
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* Minimum number of validators
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### Immediate Finality
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IBFT 2.0 has immediate finality. When using IBFT 2.0 there are no forks and all valid blocks are included in the main chain.
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Clique does not have immediate finality. Implementations using Clique must be aware of forks and chain reorganizations occurring.
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### Liveness
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Clique is more fault tolerant than IBFT 2.0. Clique tolerates up to half to the validators failing. IBFT 2.0 networks
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tolerate up to (n-1)/3 faulty nodes. For example, in an IBFT 2.0 network of:
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* 3, no bad node are tolerated
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* 4-6, 1 bad node is tolerated
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* 7-9, 2 bad nodes are tolerated
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### Speed
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Reaching consensus and adding blocks is faster in Clique networks. For Clique, the probability of a fork
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increases number as the of validators increases.
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For IBFT 2.0, the time to add new blocks increases as the number of validators increases.
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### Minimum Number of Validators
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IBFT 2.0 requires 4 nodes to be Byzantine fault tolerant.
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