Bitcoin and chains · 12 / 86 · 3 min
Layer 2s and rollups
A layer 2 tries to do the busy work elsewhere and post a summary back to a chain like Ethereum. You need to know where the money actually sits, and how long a withdrawal can wait.
A layer 2 posts a summary back to a chain. Withdrawals can wait, and someone may be able to pause them.
A worked case
A person bridges onto a rollup because the fees are pennies. They try to leave during a halt. The sequencer is down. Their coins are in the rollup's system, not in the wallet on the chain they started from, until the exit finishes.
Why they exist
The base chain gets expensive when everyone uses it directly. A rollup batches many actions into one posting. That can be cheaper. It adds a new set of operators.
Where the money sits
Often the funds are locked in a contract on the base chain, and the rollup keeps the detailed balances. If the rollup's operators stall, your withdrawal can wait. Some systems have an escape hatch. Some only promise one.
A logo that says secured by Ethereum is a claim. Read whether you can exit without the operator's permission.
The busy work moved upstairs
A rollup tries to do many transactions away from Ethereum and post a compressed record, or a proof, back to it. Arbitrum and Optimism are the names a normal person meets. In 2022 both were young, and both could be halted or upgraded by a security council or a multisig. Optimism published its own notes on the upgrade keys. The point is not that they are villains. The point is that a cheaper fee does not mean the money sits where the poster says.
Withdrawals are the test. On an optimistic rollup, a challenge period can mean you wait days to leave back to Ethereum, unless you trust a fast bridge, which is another set of signers. If the sequencer stops, you may not be able to do the ordinary thing you came for. The chain underneath is still there. Your coins are in the system upstairs until the exit works.
Read who can upgrade the bridge and how long an exit takes on a bad day. If the answer is a logo and soon, you have not finished the page.
Read it yourself
These links are the record. They are not a recommendation, and they are not instructions. A news story or a court paper can still be wrong about a detail. The check does not change because a famous name is in the story.
Apply the check
Open a question. The line is about this topic. It is not a verdict that anything is safe.
The sequencer, and whoever collects the fee.
The operator, if they can upgrade the bridge or censor withdrawals.
The exit delay, and any admin who can pause the bridge.
Check yourself
Is a layer 2 the same as holding coins on the base chain yourself?
No. There is an extra system, and an exit can take time.
After this you can ask where the funds are locked, and what happens if the operator stops.