Have you ever wondered how Ethereum blocks get made? It's not as simple as a single computer solving a puzzle anymore. Today, it's a big business.
Validators run the network. They check transactions and add them to the blockchain. But they don't just take transactions from a public queue. They want to make the most money possible.
To do this, they use a special system called MEV-Boost. This tool connects them to a hidden market. If you want to understand how the plumbing of crypto works, you must understand this system. You can find out more about crypto infrastructure at The Coin View website. We explain these systems simply.
Let's look at how this setup works. We'll see why it's both amazing and dangerous.
What is MEV and Why Does It Matter?
MEV stands for Maximal Extractable Value. It's a fancy term for a simple idea. It's the extra profit a block builder can make by changing the order of transactions.
Imagine you are standing in a line at a store. You want to buy a rare toy for ten dollars. Another person behind you sees this. They want to buy it first so they can sell it to you for twenty dollars instead.
In Ethereum, this happens every second. People write computer programs to spot these chances. These people are called searchers.
Searchers look for price differences on different exchanges. They look for liquidations. They also look for people making large trades.
Then, they create a bundle of transactions. They pay a high fee to get their bundle processed first. This is how they make their profit.
But searchers cannot put their bundles directly into a block. They need help. That's where builders come in.
Example: The Sandwich Attack
What is a sandwich attack? Let's look at a simple example.
Imagine you want to buy a token on a decentralized exchange. Let's call it Token A.
You submit your trade. You are willing to pay up to one dollar per token. This is your slippage limit.
A searcher spots your transaction in the public pool. They see that you are willing to pay more.
The searcher acts quickly. They buy Token A just before you do. This pushes the price up to ninety-nine cents.
Then, your trade goes through. You buy Token A at the higher price of one dollar.
Right after your trade, the searcher sells their tokens. They sell them at the new, higher price.
They have just made a profit from your trade. Your transaction was the filling in their sandwich.
This happens thousands of times every day. It costs regular users millions of dollars.
To make this work, searchers need their buy order first. They need their sell order right after yours.
They pay builders high fees to guarantee this order.
The Three Players in the Block Game
To understand the system, you must meet the three main players. Each has a different job.
First, we have the searchers. We just talked about them. They find the profitable trades.
Second, we have the builders. Builders are companies with powerful computers. They collect transactions from searchers and the public pool. They piece them together like a puzzle.
Their goal is to make the most valuable block possible. They want the total fees in their block to be very high.
Third, we have the validators. Validators are the official network helpers. They have locked up 32 Ether to get the right to propose blocks.
Every twelve seconds, the network selects one validator to propose a block. That validator gets to choose which block of transactions to add.
Naturally, the validator wants to choose the block that pays them the most.
But there's a big problem here. It's a problem of trust.
Why We Need a Trusted Middleman
Why can't validators and builders just talk to each other directly?
Let's think about what would happen.
A builder makes a highly profitable block. They send it to the validator.
The validator looks at the block. They see the profitable trades inside.
What stops the validator from stealing those trades? Nothing.
The validator could copy the builder's ideas. They could make their own block. They'd take all the money. The builder gets nothing.
Because of this, builders won't show their blocks to validators beforehand.
But validators also have a trust issue. They don't want to propose a block without knowing they'll get paid.
They need to be sure the builder's payment is real.
How do we solve this? We use a middleman. This middleman is called a relay.
How the MEV-Boost Relay Works Under the Hood
The relay acts like a trusted auctioneer. It stands right between the builders and the validators.
Here's the step by step process.
First, builders create their blocks. They send these blocks to the relay.
The relay checks the blocks. It makes sure they're valid. It checks how much the block pays the validator.
Second, the relay hides the contents of the block. It only shows the validator the price tag.
For example, the relay tells the validator: "This block will pay you one Ether."
Third, the validator chooses the block with the highest payment. They sign the block header. This is like signing a contract.
Once the validator signs, they're locked in. They cannot change the transactions. They must propose that specific block.
Fourth, the relay releases the full block to the network. The validator gets paid. The builder gets their trades processed.
Everyone wins, right? Well, not quite.
Why MEV-Boost Was Created
In the early days of Ethereum, validators didn't use relays. They just built their own blocks.
But this created a big problem. Only large mining pools had the skills to find MEV.
Small validators were missing out on these extra profits. This made it hard for them to compete.
It looked like Ethereum was becoming centralized. People feared that only a few big players would run the network.
To fix this, a research group called Flashbots created MEV-Boost.
They wanted to share the MEV profits with everyone. With MEV-Boost, any small validator can get these extra rewards.
They just have to install the software. It connects them to the relays.
Today, over ninety percent of Ethereum validators use MEV-Boost. It's made validating more profitable for normal people.
But it also shifted the centralization risk to the relays.
The Big Risks of Using Relays
This system works well for making money. But it creates a huge risk for Ethereum.
The first risk is centralization. Running a relay is hard work. It requires fast servers and lots of bandwidth.
It also doesn't make any money. Relays are free to use. They don't take a cut of the fees.
Because of this, only a few groups run relays. Most validators use the exact same few relays.
If these relays go down, the network can slow down.
We've seen this happen. A single relay had a bug once. It stopped sending blocks.
Validators missed their turns. The network missed blocks. It was a mess.
The second risk is censorship. Because relays are run by known companies, they must follow laws.
Some governments don't want certain transactions to go through. They might block transactions linked to smart contract mixers.
If a relay blocks these transactions, it's censoring the network.
For a long time, many Ethereum blocks went through censoring relays. This goes against the core idea of crypto. It should be open to everyone.
We see similar control in other areas of crypto. Market makers often control how tokens move. You can read about this in our piece on How OTC Desks Stop Token Unlocks From Crashing Crypto Prices. These systems keep the market stable. But they also put power in few hands.
How a Bad Relay Can Exploit the System
Can a relay act maliciously? Yes, it can.
A relay could lie to a validator. It could pretend a block pays a lot of money.
The validator signs the block header. Then, the relay reveals that the block actually pays nothing.
Or worse, the relay could steal the builder's block. It could copy the trades. Then it could send them to a friendly validator.
This is not just a theory. Researchers have found ways that relays can be manipulated.
If validators lose trust in relays, the whole system breaks.
They might stop using MEV-Boost altogether. This would mean validators make much less money.
If validators make less money, fewer people will want to secure the network.
This shows how critical these middlemen are to Ethereum's security.
How Relays Maintain Trust Today
Right now, relays work because of reputation. If a relay behaves badly, everyone will know.
Builders will stop sending blocks to it. Validators will stop using it. The relay operator would lose all their credibility.
Most relays are run by respected organizations. This includes groups like Flashbots, BloXroute, and Ultrasound Money.
They do this as a public service. They want to help the Ethereum network stay healthy.
But relying on reputation is not a long term solution. In crypto, we say: "Don't trust, verify."
We want systems that do not rely on good behavior. We want systems where bad behavior is mathematically impossible.
That is why the move to on-chain PBS is so important.
How Ethereum Plans to Fix This
Ethereum developers know that relying on these middlemen is bad. They are working on solutions.
The main plan is called Proposer-Builder Separation, or PBS.
The goal is to build the relay's job directly into the Ethereum code.
Instead of a third-party relay, the blockchain itself will handle the auction.
This would make the system trustless. Builders could submit blocks safely. Validators could select blocks without trusting a middleman.
Another idea is to use censorship resistance lists.
These lists force builders to include certain transactions. If they don't, validators will reject their blocks.
These changes will take time to build. Until then, we must rely on the honesty of a few relay operators.
Do you think Ethereum can solve its middleman problem? It's one of the biggest challenges for the network today.
Next time you send a transaction, think about the complex journey it takes. It's not just about code. It's about incentives, trust, and the struggle to keep crypto decentralized.
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