Second-layer solutions are explained in full under layer 2, which covers how they work, the main designs and their trade-offs. This page explains the longer phrase, which is common in older guides and exchange glossaries.
A second-layer solution is a protocol that sits above a base blockchain, such as Bitcoin or Ethereum, and processes transactions away from it, returning to the main chain only to settle results or resolve disputes. The base chain, often called layer 1, stays small and secure, while the second layer handles volume. The aim is to answer the scaling problem without asking every node to process every payment.
Main types include:
- Payment and state channels. Two parties lock funds on-chain and trade signed updates off-chain, as in the Lightning Network.
- Rollups. Transactions are batched and posted to the base chain with fraud proofs or validity proofs, as in an optimistic rollup.
- Plasma and related designs. Child chains that commit summaries to the main chain, now largely replaced by rollups.
Sidechains, which have their own validators and security, are sometimes grouped with second-layer solutions but do not inherit the base chain's security in the same way. The general family is also called off-chain scaling or scaling solutions.