BlockchainIntermediate#Scaling#Infrastructure
Layer 2 (L2)
L
Definition
A protocol layer that executes transactions outside an L1 while using that L1 for some combination of data availability, proofs, dispute resolution, or settlement. Fees, finality, bridges, and withdrawal paths depend on the specific L2 design.
Source reviewed
- Ethereum.org: Optimistic rollups opens in a new tab
Supports: Explains offchain execution, onchain data publication, fraud proofs, challenge periods, sequencer limits, withdrawals, and L1 settlement for optimistic rollups.
- Ethereum.org: Zero-knowledge rollups opens in a new tab
Supports: Explains validity proofs, L1 verification, data availability, and the implementation-specific design of ZK rollups.
Concept Diagram
Key Takeaways
1
L2 describes a family of designs, not one common fee, finality, or security promise
2
Rollups can batch execution while publishing data, commitments, or proofs to Ethereum
3
Optimistic and ZK rollups use different proof and timing mechanisms
4
Bridge, token, sequencer, withdrawal, and recovery assumptions must be checked per network
Practical Example
A user bridges a token to an L2. Before signing, they compare the official bridge contract, target chain, token address, fee asset, expected withdrawal path, and the application's recovery guidance. The user does not assume that a fast L2 confirmation means the same asset is immediately settled or withdrawable on Ethereum Mainnet.
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Related Terms
Blockchain
Data Availability (DA)Assurance that data needed for a specified verification process was published and can be accessed under that system's rules. It is distinct from permanent historical retrievability.
Blockchain
SequencerA node in a Rollup (L2) responsible for ordering transactions before they are batched and sent to the L1 (Ethereum).
Blockchain
Base Layer (Layer 1)A blockchain's own consensus and settlement layer. The label describes where that protocol processes and orders transactions; security, finality, data availability, and scaling guarantees differ by chain and design.
Blockchain
ShardingA family of scaling designs that divide data or execution work across subsets of a network; the exact meaning depends on the protocol.
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