Roadmap › Blockchain & Web3 Fundamentals › Module: Ethereum in Depth
Lessons in this course (15)
9. Scaling: layer 1, layer 2, rollups and sidechains
Intermediate★ Must knowLesson 9 of 15
- Layer 1 — the base chain (Ethereum, Bitcoin, Solana).
- Layer 2 — executes transactions off the main chain and posts data/proofs to L1, inheriting its security:
- Optimistic rollups (Arbitrum, Optimism, Base): assume transactions are valid; anyone can submit a fraud proof during a challenge window (~7 days for withdrawals to L1).
- ZK rollups (zkSync Era, Starknet, Scroll, Linea, Polygon zkEVM): post validity proofs (zero-knowledge proofs); faster finality, more complex.
- EIP-4844 blobs (Dencun, 2024) made L2 data much cheaper → L2 fees often cents or less.
- Sidechains (Polygon PoS, Gnosis Chain): separate chains with their own consensus and bridges (not L1 security).
- State channels (Bitcoin Lightning Network): off-chain payments between parties, settle on-chain.
- Bridges move assets between chains — historically the biggest hack targets (Ronin $625M in 2022, Wormhole $325M in 2022).