What Is a Layer 2?
How L2s inherit Layer 1 security while processing transactions elsewhere.
Borrowing a Layer 1's security
A Layer 2 is a protocol built on top of a Layer 1 that does most of its transaction processing elsewhere, then periodically checks in with the base layer. It doesn't need its own army of validators from scratch - it leans on the L1's existing security instead.
That's the key difference from just building a brand-new, separate blockchain: a well-designed Layer 2 is only as trustworthy as its connection back to the L1 lets it be.
The basic recipe
A component called a sequencer collects transactions and orders them, much faster and cheaper than the base layer could on its own. Periodically, a summary of what happened - compressed data, and often a proof - gets posted back to the Layer 1.
Once that summary is on the L1, it inherits the L1's guarantees: the data is public, and the L1's own security now backs up the L2's history. Different Layer 2 designs differ mainly in how they prove that summary is honest - the subject of the next lesson.
Why fees drop
Posting to a Layer 1 costs money - it's competing for the same limited block space as everyone else. A Layer 2 batches hundreds or thousands of transactions into one L1 posting, so that cost gets split across everyone in the batch instead of paid individually.
That's the practical payoff for users: transactions that might cost dollars directly on the L1 can cost fractions of a cent on a well-used Layer 2.
Remember
You're still ultimately paying for L1 block space - just your tiny slice of one shared posting instead of a whole transaction's worth.
Self-check
Check your understanding
Try each question before opening the answer.
What makes a Layer 2 different from an entirely separate, standalone blockchain?
- A.L2s don't have their own transactions
- B.L2s periodically settle back to a Layer 1 and inherit its security
- C.L2s can't be hacked
- D.L2s don't charge any fees
Reveal answer
B. L2s periodically settle back to a Layer 1 and inherit its security
The defining trait of a Layer 2 is that it leans on an underlying Layer 1 for security, rather than securing itself from scratch.
What does a Layer 2's sequencer do?
- A.Mines the Layer 1's blocks
- B.Orders and batches Layer 2 transactions before they're posted to Layer 1
- C.Stores users' private keys
- D.Sets the price of gas on Layer 1
Reveal answer
B. Orders and batches Layer 2 transactions before they're posted to Layer 1
The sequencer is the component that collects and orders L2 transactions ahead of posting a summary to the base layer.
Why are Layer 2 transaction fees typically much lower than paying the Layer 1 directly?
- A.L2s are exempt from paying for L1 block space
- B.The cost of one L1 posting is split across many batched L2 transactions
- C.L2 validators work for free
- D.L1 block space is unlimited
Reveal answer
B. The cost of one L1 posting is split across many batched L2 transactions
Batching means many users share the cost of a single L1 posting instead of each paying for their own.
Continue this track