Scaling Solutions: Layer 2s, Bridges, and Modular Architecture

What you'll learn

• The Scalability Trilemma
• What Are Layer 2s?
• EIP-4844 / Dencun: The Game-Changer
• Modular Blockchain Architecture
• For Deeper Reading

Key terms

Layer 1 (L1)

The base blockchain network providing final settlement and security. Bitcoin and Ethereum are the major L1s.

Layer 2 (L2)

A secondary network built on top of L1 that improves scalability while inheriting L1 security. Rollups are the dominant form.

Rollup

A Layer 2 scaling solution that batches many transactions into a single Layer 1 transaction. Optimistic rollups (Arbitrum, Optimism, Base) and ZK rollups (zkSync, StarkNet, Linea, Scroll) are the main types.

Optimistic rollup

Assumes transactions are valid; uses a 7-day fraud proof window allowing challenges. Arbitrum, Optimism, Base.

ZK rollup

Uses zero-knowledge cryptographic proofs (SNARKs or STARKs) to prove transaction validity. Faster finality on L1; cheaper data; smaller proofs. zkSync, StarkNet, Linea, Scroll.

EIP-4844 / Proto-Danksharding (Dencun)

Ethereum upgrade activated March 13, 2024. Introduced blob-carrying transactions, reducing L2 posting fees ~90%.

Zero-knowledge proof

A cryptographic method to prove something is true without revealing the underlying information. Powers ZK rollups and privacy projects.

Modular blockchain

Architecture where execution, settlement, consensus, and data availability are handled by specialized layers rather than one chain doing everything.

Data availability (DA)

The property that all data required to verify a block is publicly available. Celestia, EigenDA, and Avail are dedicated DA layers.

EigenLayer

Ethereum restaking protocol. Restaked ETH provides shared security to Actively Validated Services (AVSs). Slashing live April 17, 2025.

Sidechain

A separate chain with its own consensus that bridges to a parent chain. Less secure than rollups (does not inherit parent chain security). Polygon PoS is a leading example.

Application chain (app-chain)

A blockchain dedicated to a single application. dYdX (on Cosmos), Hyperliquid, opBNB are examples. Trades broader composability for application-specific optimization.