What is a layer 2?

Blockchains such as Ethereum, Solana and Bitcoin are called layer 1: they settle transactions on their own. Ethereum deliberately keeps its blocks small so that many people can run a node, which means space is scarce and fees rise when demand peaks. Layer 2 networks move most of the work elsewhere and use Ethereum only as the final record. For background on Ethereum itself, see our page on buying Ethereum.

How does a rollup work?

Most layer 2 networks are rollups. They gather thousands of transactions, execute them, and post the data in a batch to Ethereum. Users share the cost of that single batch instead of each paying for space on the main chain. Since Ethereum's March 2024 upgrade introduced a cheaper data format known as blobs, posting those batches has become much less expensive.

There are two main designs:

• Optimistic rollups assume batches are valid and allow a challenge window in which anyone can prove fraud. Arbitrum One, OP Mainnet and Base use this approach.
• Zero-knowledge rollups attach a cryptographic proof to every batch showing that the computation was correct.

On the best-known layer 2 networks, fees are paid in ETH. How those fees are calculated is explained in what gas fees are.

Which layer 2 networks will you see?

When you withdraw from an exchange, these three often appear in the network list:

• Arbitrum One
• Base, developed by Coinbase
• OP Mainnet, from the Optimism Collective

Polygon is often grouped with them, although its main chain works differently. Each of our network pages lists the coins available there and which licensed exchanges let you withdraw to it. Not every exchange supports every layer 2, so check before you choose a wallet set-up.

Are layer 2 networks as secure as Ethereum?

Not always, and not yet. Many still rely on a single operator to order transactions, or on a council that can upgrade the system at short notice. L2BEAT, an independent research site, rates each network on how far it has progressed towards inheriting Ethereum's security. Moving funds between Ethereum and a layer 2 goes through a bridge, and bridged assets may be a wrapped version of the original; see what a wrapped token is.

What to check before withdrawing

ETH on Base and ETH on Arbitrum share a name but live on separate networks. Your receiving wallet or exchange must support the network you select, otherwise the funds will not arrive where you expect; our guide on sending crypto to the wrong network explains what you can do. The network overview lists every network we track, and the comparer shows which licensed exchange gives you the most ETH for your euros before you withdraw.