The Blockchain Trilemma
First defined by Vitalik Buterin, the blockchain trilemma asserts that a blockchain can achieve only two of three properties: decentralization, security, and scalability. To scale networks, developers created Layer 2 scaling layers.
Layer 1: The Foundation Layer
Layer 1 (L1) refers to the base network architecture. Examples include Bitcoin, Ethereum, and Solana. L1 networks settle all transactions, enforce consensus rules, and maintain the primary ledger state. Because L1s prioritize security and decentralization, they often experience network congestion and high transaction fees.
Layer 2: Scaling Solutions
Layer 2 (L2) is a secondary framework built on top of an existing blockchain. L2s process transactions off-chain, bundle them together, and submit the compressed proof back to the L1 ledger. This reduces fees and increases throughput while inheriting the L1's security:
- Optimistic Rollups: Assume transactions are valid by default. Validators can dispute fraudulent transactions within a challenge window (e.g., Arbitrum, Optimism).
- Zero-Knowledge (ZK) Rollups: Generate cryptographic proofs (ZK-SNARKs) off-chain that verify transaction accuracy immediately, allowing instant on-chain finality.