Description

Layer-2 networks, or 'rollups', are protocols built on top of a Layer-1 blockchain such as Ethereum. They are designed to process transactions off the main chain to increase speed and reduce costs while inheriting the security guarantees of the Layer-1. Users utilise Layer-2s to access decentralised finance (DeFi) and gaming applications with lower fees. Appchains are application-specific blockchains that may function similarly or as standalone chains with specific bridges.

Risks

Dependency on Layer-1. Layer-2 networks are entirely dependent on their underlying Layer-1 for finality and security. If the Layer-1 network suffers an outage, a reorganisation, or a censorship attack, the Layer-2 network will be directly affected. The Layer-2 cannot exist or secure funds without the liveness and security of the Layer-1.

Sequencer Centralisation. Many Layer-2s currently rely on a single centralised 'sequencer' to order and process transactions. This sequencer is often operated by the project development team and creates a single point of failure. If the sequencer goes offline, the network may halt and prevent you from transacting. If the operator acts maliciously, they could potentially censor your transactions or exploit the order of trades for profit (MEV). While many Layer-2s plan to decentralise their sequencers, this remains a future roadmap item rather than a current reality for many.

Bridge Security and Exit Timelines. To use a Layer-2, you must 'bridge' assets from the Layer-1. The smart contracts that hold these bridged assets are frequent targets for exploits. Additionally, moving funds back from a Layer-2 to the Layer-1 can be subject to long waiting periods. For 'optimistic rollups', this withdrawal period can last roughly seven days to allow for fraud proofs to be challenged. You may be unable to access your funds on the main chain during this time unless you use third-party liquidity providers, which introduce their own risks and fees.

Upgradeability and Key Controls. Many Layer-2 networks are still in an experimental phase and developers often retain 'admin keys' or 'multisig controls' that allow them to upgrade the smart contracts instantly. While this allows for quick bug fixes, it also means the team could theoretically alter the protocol in a way that compromises user funds without community consent or prior warning.

Data Availability Risks. Layer-2s must post transaction data to the Layer-1 to ensure security and state reconstruction. If the Layer-2 fails to post this data correctly, or if the data becomes unavailable due to technical failures, users may be unable to reconstruct the state of the Layer-2 and could lose access to their funds permanently.