Layer 1 / Layer 2

In blockchain architecture, Layer 1 (L1) refers to the base blockchain protocol itself — the fundamental network that handles consensus, security, and data availability. Bitcoin, Ethereum, Solana, and Avalanche are all Layer 1 blockchains. Each L1 makes different design trade-offs between decentralization, security, and scalability — a tension known as the "blockchain trilemma," which suggests that a blockchain can optimize for only two of these three properties simultaneously.

Layer 2 (L2) solutions are secondary frameworks built on top of Layer 1 blockchains to improve scalability — primarily by processing transactions off the main chain while still inheriting its security guarantees. The main L2 approaches include: Optimistic Rollups (Arbitrum, Optimism, Base) that assume transactions are valid unless challenged; Zero-Knowledge Rollups (zkSync, StarkNet) that use cryptographic proofs to verify transaction validity; State Channels (Lightning Network for Bitcoin) for repeated transactions between fixed parties; and Sidechains (Polygon PoS) that run parallel chains with their own consensus.

The L1/L2 relationship is crucial for blockchain scalability. Ethereum's "rollup-centric" roadmap explicitly positions L2s as the primary scaling solution, with the L1 providing security and data availability. This modular approach contrasts with monolithic L1s like Solana that aim to handle all transactions on a single chain. As of 2026, the leading L2s collectively process more transactions than Ethereum mainnet at a fraction of the cost, with total value bridged to L2s exceeding $25 billion.