Subnet (Blockchain)

In blockchain, a subnet, short for subnetwork, is a group of validators that work together to run one or more blockchains of their own while remaining connected to a larger parent platform. Each subnet can set its own rules, including who may validate, which token pays fees and which virtual machine executes transactions, while drawing on the parent platform's software and network of users. Subnets let projects launch dedicated chains for a single application, a company or a community without building a network from scratch.

The term is most closely linked to Avalanche, where subnets were a core feature from its launch, and where in 2024 they began to be called Avalanche L1s. It is also used by Bittensor for its specialized networks for machine learning tasks, and in ordinary computer networking for a slice of an internet address range. Subnets are one answer among several to the question of how to scale blockchains, alongside parachains, rollups and appchains.

Think of a large shopping centre. The centre provides the land, the roads, the security and the signs that bring in visitors. Inside it, each shop sets its own opening hours, prices and staff rules. A busy shop does not slow down the one next door, and a new shop does not need to build its own car park.

A subnet is a shop in that centre. The parent platform supplies common software and a way for chains to find and talk to each other. The subnet supplies its own validators, its own rules and often its own token. If one subnet becomes congested, for example during a popular game launch, the traffic stays inside that subnet rather than raising fees for everyone else.

Avalanche is organized around a Primary Network made up of three built-in chains, one of which, the Platform Chain or P-Chain, keeps track of validators and subnets. Creating a subnet involves registering it on the P-Chain, choosing a set of validators and launching one or more blockchains whose rules those validators enforce. A subnet's chains may run a version of the Ethereum Virtual Machine or a custom virtual machine.

• Sovereignty. Each subnet chooses its own fee token, gas settings and upgrade schedule.
• Optional permissioning. A subnet can be open to anyone or limited to approved validators and users, which appealed to companies and financial institutions testing permissioned blockchains.
• Separate capacity. Because each subnet processes its own transactions, activity on one does not consume the capacity of others.
• Messaging. Avalanche provides a native messaging system that lets subnets send messages and assets to one another, a form of blockchain interoperability.

Early on, validators of any subnet also had to validate the Primary Network, which required staking a substantial amount of AVAX through proof of stake. An upgrade activated in December 2024, known as Etna, changed this model so that validators of these chains no longer need to validate the Primary Network and instead pay an ongoing fee, lowering the cost of launching a chain. Around the same time, Avalanche's own materials moved from "subnet" to "Avalanche L1" to stress that each such chain is an independent layer 1 blockchain.

Bittensor uses the word for separate competitive markets within its network, each focused on a task such as text generation, data scraping or prediction. Miners in a subnet produce outputs, validators score them, and rewards in the network's token are distributed according to those scores. The idea is similar in spirit to Avalanche's, in that each subnet has its own rules within a shared system, but the technology and purpose differ. Other platforms use related ideas under different names, such as Polkadot's parachains and the independent chains built with Cosmos software.

Subnets have been used for blockchain games that need fast, cheap transactions, for decentralized exchanges that want control over block space, and for institutional pilots of real-world asset tokenization, where identity checks for validators and users may be required. Because a subnet can pick its own token for fees, a game can let players pay in its own currency rather than in AVAX.

Critics argue that subnets can fragment liquidity and users across many small chains, each with fewer validators and therefore weaker security than the main network. A subnet with a handful of validators may be easier to attack or to censor than a large public chain. Moving assets between subnets adds complexity and the usual risks of bridging. Some subnets launched with fanfare and then saw little use, raising questions about demand for dedicated chains compared with deploying applications on existing networks or scaling solutions such as rollups. Changes in terminology and economics, including the 2024 rebranding and validator changes, have also made the model harder to follow for newcomers.

• Avalanche