What is layer 2?

A network built on top of a base blockchain to process transactions faster and cheaper, settling periodically to the main chain.

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A network built on top of a base blockchain to process transactions faster and cheaper, settling periodically to the main chain.

Arbitrum, Optimism, and Base are layer 2s on Ethereum. Assets on a layer 2 must be sent to layer 2 addresses, not main-chain addresses.

That last sentence is where money is lost. The address format is identical to Ethereum's, so a wallet will happily accept a main-chain address for a layer 2 withdrawal and the transaction will succeed on the wrong network. Exchanges list the network separately from the asset for exactly this reason.

How it works

A layer 2 executes transactions on its own network and posts the results back to the base chain, which is what makes it a layer 2 rather than a separate blockchain. The base chain provides the security and the final record; the layer 2 provides the throughput.

Two designs dominate. An optimistic rollup posts transaction data to the base chain and assumes it is valid, allowing a challenge window in which anyone can submit a fraud proof. Because a withdrawal has to outlast that window, the standard challenge period on the major optimistic rollups is seven days, which is why moving funds back to Ethereum through the canonical bridge takes a week unless you use a third-party fast bridge that fronts the money for a fee.

A validity rollup, usually called a zk-rollup, posts a cryptographic proof that the transactions were executed correctly. There is nothing to challenge, so withdrawals settle as soon as the proof is verified.

Both post their data to the base chain, and since the introduction of blob transactions through EIP-4844 that data goes into a cheaper temporary space rather than into regular transaction calldata. That change is the main reason layer 2 fees fell substantially.

Most rollups today run a single sequencer, operated by the team, which orders transactions. It cannot steal funds, because the base chain enforces the rules, but it can go down or censor, and forced-inclusion mechanisms through the base chain are the fallback.

Example

Illustrative walkthrough. You buy ETH on an exchange and withdraw it. The exchange asks which network. Choosing Ethereum sends it to the main chain, where a transfer might cost a few dollars. Choosing Arbitrum sends it to that layer 2, where the same transfer costs a fraction of a cent, and the funds appear in the same address on a different network. If you later want them back on Ethereum through the canonical bridge, the withdrawal enters the challenge period and completes about seven days later. A fast bridge would deliver in minutes for a fee, because a liquidity provider is fronting you the funds and waiting out the week themselves.

Why it matters when you buy

Withdrawal network choice is a real cost decision and a real risk decision. Not every exchange supports every layer 2, and sending to a network the receiving venue does not support can make funds unrecoverable. Check what each venue supports on the exchange pages, compare withdrawal costs on the fee comparison, and see layer 1 versus layer 2 and sending crypto across chains for the mechanics.

Questions

Is my Ethereum address the same on a layer 2?

Yes, and that is the hazard. The address is valid on every compatible network, so choosing the wrong one sends funds somewhere real that the recipient may not control.

Why does withdrawing to Ethereum take seven days?

On an optimistic rollup, the challenge window has to expire before a withdrawal is final. Validity rollups do not have this delay, and fast bridges avoid it by advancing you the funds.

Are layer 2 funds as safe as main-chain funds?

The base chain enforces correctness, but you additionally depend on the sequencer's availability and, in most cases, on upgrade controls held by the operating team. That is a different risk profile, not an identical one.

Guides that use this term

  • Gas Fees Explained: Why They Change and How to Pay Less

    A gas fee is the amount of computational work your transaction uses multiplied by the price you pay per unit of that work, and it changes minute to minute because the price rises automatically when blocks are fuller than the network's target.

  • How to Use a Block Explorer to Check a Transaction

    A block explorer is a public search engine for a blockchain, and you check a transaction by pasting its hash into the search box and reading three fields: the status, the number of confirmations, and the receiving address.

  • Layer 1 vs Layer 2: What the Difference Means When You Buy and Move Crypto

    A layer 1 is a blockchain that settles its own transactions, while a layer 2 is a separate network that processes transactions off the main chain and posts them back to the layer 1 for settlement, which matters to you because the same token on two networks costs different amounts to move and does not share a deposit address.

  • How to Send Crypto Across Chains Without Losing It

    Moving crypto between chains means either routing it through an exchange that accepts deposits on one network and withdrawals on another, or using a bridge that locks the asset on the source chain and issues a wrapped version on the destination, and in both cases the mistake that costs people money is picking the wrong network on the send screen.

  • How to Move Crypto Off an Exchange to Your Own Wallet

    To move crypto off an exchange, set up a wallet you control, copy its receiving address for the exact network the exchange is sending on, send a small test amount first, wait for it to confirm, then send the rest and pay the network fee the exchange quotes.