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Research · ICP

Subnets: nodes, consensus and replication

The Internet Computer is not a single blockchain. It is a network of independent blockchains called subnets, each running its own consensus protocol over its own node set. That structure is what lets the platform scale without asking every node to hold every canister.

Last reviewed 2026-09-21Source: ICP Developer Docs — Network overview, subnets and node typesSubnet composition and node counts change through NNS proposals; the figures here describe the architecture rather than a snapshot of the current network.

What a subnet is

A subnet is a group of node machines that run their own instance of the Internet Computer Protocol. Each subnet maintains its own chain, reaches its own consensus, and executes the canisters assigned to it. The subnets are connected by a protocol-level routing layer, so a canister on one subnet can call a canister on another, but each subnet's state is its own.

This is the structural difference from a single-chain network. On Bitcoin, every full node validates every block, and the chain's capacity is bounded by what an ordinary machine can verify. On the Internet Computer, a canister is replicated across the nodes of one subnet rather than across the whole network, so adding subnets adds capacity without asking any individual node to hold more. The trade-off is that a canister's security is the security of its subnet's node set, not of the entire network.

Replication is what makes a canister tamperproof. Every node in the subnet holds a copy of the canister's state and executes the same messages, and consensus requires a supermajority to agree before a message's effects are finalised. No single node can unilaterally change a canister's state, and a node that goes offline or turns malicious is outvoted rather than trusted.

Consensus and finality

Each subnet runs a consensus protocol that orders the messages it receives and finalises them into blocks. The documentation describes subnets producing one finalised block per round, approximately every second, with cryptographic rather than probabilistic finality. Once a block is finalised, the messages it contains cannot be reordered or removed by a later block.

That is a different settlement model from Bitcoin's. A Bitcoin transaction gains assurance as confirmations accumulate, and the convention of waiting for six confirmations is a probabilistic judgement rather than a protocol rule. On the Internet Computer, finality arrives at a defined moment: the round in which the block is agreed. The confirmations and settlement page covers the Bitcoin side of that contrast.

Consensus is also where the network's threshold cryptography enters. A subnet holds a threshold key whose shares are distributed across its nodes, and a response signed by that key is a statement the subnet as a whole has agreed to. The chain-key cryptography page explains how that key is generated, used and re-shared.

Subnet types

Not every subnet serves the same purpose, and the network operates several kinds. Application subnets host ordinary canisters and are the default destination for a deployed application. System subnets run the network's own infrastructure: the Network Nervous System, the cycles minting canister, the Bitcoin integration canisters and the threshold-signing subnets that hold the master keys.

The signing subnets are the clearest example of a purpose-built subnet. Threshold ECDSA and Schnorr keys are held on dedicated subnets with a higher replication factor than a standard application subnet, because the cost of a compromised signing key is higher than the cost of a compromised application canister. The documentation notes that the test keys reside on a smaller subnet while the production keys reside on a larger one, and that the subnet holding the key — not the subnet of the calling canister — determines the cost of a signature.

A third category has emerged more recently: subnets provisioned for a single owner rather than for the public network. Those are described on the cloud engines page, which is careful to separate what is deployed from what is still being built.

Sources and references

The subnet architecture, the consensus model and the subnet types are described from the Internet Computer's own documentation. Where a figure would change with network governance, the page describes the mechanism rather than quoting a number.

  • Subnets as independent blockchains. ICP Developer Docs, Network overview: describes subnets, node composition, replication and roughly one-second block finality.
  • Threshold-signing subnets and key identifiers. Internet Computer, Threshold signatures: explains that production keys reside on a larger subnet than test keys, and that the key's subnet determines the signature cost.
  • Protocol canisters and system subnets. ICP Developer Docs, Protocol canisters: lists the system canisters, including the Bitcoin integration canisters and the cycles minting canister.

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