A subnet (subnetwork) is a collection of nodes that run their own instance of the consensus algorithm to produce a subnet blockchain that interacts with other subnets of the IC using chain key cryptography.
The IC is designed to be highly scalable and efficient in terms of hosting and executing canister smart contracts. The top-level building blocks of the IC are subnetworks, or subnets: the IC as a whole consists of many subnets, where each subnet is its own blockchain that operates concurrently with and independently of the other subnets (but can communicate asynchronously with other subnets). Each subnet hosts canister smart contracts, up to a total of hundreds of gigabytes of replicated storage. A subnet consists of node machines, or nodes. Each node replicates all the canisters, state, and computation of the subnet using blockchain technology. This makes a subnet a blockchain-based replicated state machine, that is, a virtual machine that holds state in a secure, fault-tolerant, and non-tamperable manner: the computations of the canisters hosted on a subnet will proceed correctly and without stopping, even if some of the nodes on the subnet are faulty (either because they crash, or even worse, are hacked by a malicious party) New subnets can be created from nodes added to the IC to scale out the system, analogous to how traditional infrastructures such as public clouds scale out by adding machines. Such a scale-out architecture is rather the exception than the rule in the blockchain space and allows for limitless scaling, i.e., combining the security and resiliency properties of blockchains with the scalability properties enjoyed by the public cloud.
List of Subnets
All of the subnets, with their corresponding topologies and activities are listed on the IC dashboard: ICP subnets.