Layer 2

If you've ever paid a surprisingly high fee to move tokens on a busy blockchain, you've felt the problem Layer 2s are trying to solve. These networks sit on top of a main blockchain and take on most of the work, so you can transact quickly and cheaply while still relying on the security of the chain underneath.

What Does Layer 2 Mean?

A Layer 2 is a scaling solution built on top of a Layer 1 blockchain like Ethereum or Bitcoin. Instead of recording every single transaction directly on the main chain, a Layer 2 processes transactions on its own network and then posts a compressed summary or proof back to the Layer 1.

Imagine a busy restaurant where every customer pays the cashier one at a time. The line gets long fast. Now imagine each table runs a tab and pays one combined bill at the end of the meal. The restaurant still gets paid in full, but the cashier handles far fewer transactions. Layer 2s work like that tab: many small actions get bundled and settled together.

How Layer 2 Networks Work

Different Layer 2s use different techniques, but they share the same goal: move activity off the main chain while keeping it secure. The Layer 1 acts as the final judge if anything goes wrong.

Rollups

Rollups are the most common type of Layer 2 on Ethereum. They "roll up" hundreds or thousands of transactions into a single batch and post that batch to the Layer 1. Because the cost of posting is shared across many users, each person pays a much smaller fee.

• Optimistic rollups: These assume transactions are valid by default. There's a challenge window during which anyone can submit a fraud proof if they spot a bad transaction. Withdrawals back to the Layer 1 can take several days because of this window.
• ZK rollups: These use [zero-knowledge proofs](/glossary/zero-knowledge-proof) to mathematically prove that every batch is valid. Because validity is proven upfront, withdrawals can often finalize faster.

Payment Channels

Payment channels let two parties open a channel, transact with each other many times off-chain, and only record the opening and closing balances on the main chain. The Lightning Network on Bitcoin is the best-known example.

Sidechains

Sidechains are separate blockchains connected to a main chain by a bridge. They have their own validators and security model, so strictly speaking many people don't count them as true Layer 2s. The key difference is whether the network inherits its security from the Layer 1 or relies on its own.

Why Layer 2s Matter

Popular Layer 1 blockchains can get congested. When demand is high, gas fees rise and transactions slow down. Layer 2s help by taking pressure off the base layer.

• Lower fees: Sharing settlement costs across many users makes everyday transactions far cheaper.
• Faster confirmations: Transactions on a Layer 2 usually confirm in seconds.
• Inherited security: Rollups rely on the Layer 1 for final settlement, so they benefit from its security.
• Room to grow: Layer 2s let blockchains support more users and apps without changing the base layer drastically.

Examples of Layer 2 Networks

On Ethereum, well-known Layer 2s include Arbitrum and Optimism (optimistic rollups) and networks like zkSync and Starknet (ZK rollups). On Bitcoin, the Lightning Network enables fast, low-cost payments. Many of these networks use ETH or BTC for fees, while some also have their own tokens for governance.

Each Layer 2 has its own ecosystem of apps, including decentralized exchanges, lending platforms, games, and NFT marketplaces. Some exchanges and wallets let you deposit and withdraw directly on a Layer 2, which can save you a bridging step.

Risks and Trade-Offs

Layer 2s are powerful, but they come with their own considerations. Understanding them helps you use these networks more safely.

Bridging Risk

To move funds between a Layer 1 and a Layer 2, you often use a bridge. Bridges are complex smart contracts, and some have been targeted by hackers in the past. Stick to official or well-established bridges and start with small amounts.

Centralization

Many Layer 2s still rely on a single operator, called a sequencer, to order transactions. Most projects plan to decentralize over time, but it's worth knowing that some networks are still in earlier stages.

Choosing the Wrong Network

Tokens on a Layer 2 live at addresses that often look identical to Layer 1 addresses. If you send funds on the wrong network, or to a service that doesn't support that Layer 2, they may be delayed or hard to recover. Always confirm the network on both ends before sending.

How to Start Using a Layer 2

Getting started is usually simple. Many popular wallets support Layer 2 networks, and you can switch between them in the network menu. You can fund a Layer 2 by bridging from the main chain or by withdrawing directly from an exchange that supports it. Keep a small amount of the network's fee token so you can pay for transactions. Before moving a large balance, try a small test transaction first to confirm everything arrives where you expect.

Useful Links

• What are Layer 2 solutions?
• Can the blockchain trilemma be solved?
• What is zero-knowledge?
• What is Ethereum?