Layer 2: Making Blockchains Fast
The scalability problem
Ethereum processes about 15-30 transactions per second. That is enough for a few thousand users, but not for millions. When too many people try to transact at once, fees spike and transactions slow down.
Layer 2 (L2) networks solve this by moving most of the work off the main chain (Layer 1) while still using Ethereum for security.
How rollups work
A rollup is the most common type of Layer 2. It processes transactions on its own chain, bundles them together, and posts a compressed summary back to Ethereum.
Think of it like a mail service. Instead of each person driving to the post office (Ethereum) individually, a mail carrier (the L2) collects letters from the neighborhood, loads them into one truck, and makes a single trip. The post office still handles the final delivery — but with far less traffic.
There are two types:
Optimistic rollups
Used by: Arbitrum, Optimism, Base
Assume all transactions are valid by default. If someone suspects fraud, they can submit a fraud proof during a 7-day challenge window. If the fraud proof is valid, the transaction is reversed and the cheater loses their bond.
The trade-off: withdrawing money from an optimistic rollup to Ethereum takes 7 days (the challenge period). Third-party bridges can speed this up for a fee.
ZK (Zero-Knowledge) rollups
Used by: zkSync, StarkNet, Polygon zkEVM
Generate a cryptographic proof (called a validity proof) that mathematically proves all transactions in the batch are correct. No waiting period. No trust needed.
The trade-off: generating ZK proofs requires significant computing power, making the technology more complex to build. But withdrawals can be much faster since the proof guarantees correctness.
Cost comparison
| Operation | Ethereum L1 | Arbitrum | Base |
|---|---|---|---|
| ETH transfer | $0.50-5 | $0.01-0.10 | $0.001-0.01 |
| Token swap | $5-50 | $0.10-0.50 | $0.01-0.10 |
| NFT mint | $10-100 | $0.20-1.00 | $0.02-0.20 |
These are approximate ranges and vary with network congestion. The key point: L2s are 10-100x cheaper for the same operations.
Key takeaways
- Layer 2 networks process transactions off Ethereum's main chain, then settle back to it.
- Optimistic rollups (Arbitrum, Optimism, Base) assume validity, with a 7-day challenge window.
- ZK rollups (zkSync, StarkNet) prove validity with math — no challenge period needed.
- L2s reduce costs by 10-100x while inheriting Ethereum's security.
- To use an L2, you bridge your assets from Ethereum using a smart contract.
Quiz: Layer 2: Making Blockchains Fast
1 / 5Why does Ethereum need Layer 2 networks?