In this lesson you will learn to:
- Describe what a node does.
- Follow a transaction from creation to inclusion in a block.
- Explain why many independent nodes make a network resilient.
Every node checks everything
A node is a computer running the blockchain's software. A full node keeps its own copy of the entire record and independently checks every transaction and every block against the rules. It does not take anyone's word for anything.
This is the practical meaning of "trustless": not that nobody is trusted, but that each participant can verify the rules for themselves instead of relying on a central authority.
A network of peers
Nodes connect directly to a handful of other nodes, which connect to others, forming a peer-to-peer network. There is no central server. When a node learns something new, it passes it on to its peers, who pass it on to theirs. This is called gossip, and within seconds a message can reach nodes all over the world.
The journey of a transaction
- Creation. Software holding the right private key builds a transaction and signs it.
- Broadcast. The transaction is sent to one or more nodes.
- Checking. Each node verifies the signature and the rules — for example, that the value being moved exists and has not already been used.
- Waiting. Valid transactions wait in each node's mempool (memory pool), a waiting room for transactions not yet in a block.
- Inclusion. A participant chosen by the consensus method assembles waiting transactions into a new block.
- Propagation. The new block is gossiped across the network. Each node checks it and, if valid, adds it to its copy of the chain.
Because each node checks independently, an invalid transaction or block is simply dropped by honest nodes, wherever it comes from.
Fees and priority
Blocks have limited space. On most public blockchains, transactions include a small fee, and those assembling blocks tend to include higher-fee transactions first. When many people want to use the network at once, fees rise and waiting times grow. This is a design choice that shapes how the network behaves under load.
Why many nodes matter
The more independent nodes there are, spread across different countries, owners and internet providers, the harder it is to censor transactions, shut the network down or quietly change the rules. If one node goes offline, the others carry on. This resilience is one of the main reasons for the distributed design — and it depends on ordinary participants continuing to run nodes.
Light clients
Not every device can store the whole chain. Light clients keep only block headers and ask full nodes for proofs about specific transactions, using the Merkle proofs from lesson 3.1. They trust a little more, but stay far more independent than simply asking one company's server.
Key takeaways
- A node runs the software, keeps a copy of the record and checks all the rules itself.
- Nodes pass transactions and blocks to each other in a peer-to-peer network.
- Valid transactions wait in the mempool until they are included in a block.
- Many independent nodes make the network hard to censor or shut down.
Check yourself
What does a full node do with a new block?
It checks the block and every transaction in it against the rules, and adds it to its copy only if valid.
What is the mempool?
A node's waiting area for valid transactions that have not yet been included in a block.
What does "trustless" mean in practice?
Participants can verify the rules themselves instead of relying on a central authority.
Sources
This lesson is for general education about how the technology works. It is not a recommendation to acquire, sell or hold any crypto-asset and is not financial advice.