# Messaging Between Nodes

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*Messages are broadcast on a best effort basis, and nodes can leave and rejoin the network at will, accepting the longest proof-of-work chain as proof of what happened while they were gone.*

\- Satoshi Nakamoto, Bitcoin Whitepaper

In the Bitcoin network, messages are broadcast on a **best-effort basis**, allowing nodes to **leave and rejoin the network at will**. When a node receives a new transaction, it **automatically broadcasts it to all nodes with which it has a peer connection**. This practice reduces the time required for other nodes to validate a block that includes the transaction, thereby enhancing the likelihood of quick validation.

Nodes accept the **first-seen version of a transaction as the valid version** and consider any subsequent transaction attempting to spend the same inputs as an attempt at double-spending, therefore, invalid. Similarly, when it comes to block announcements, **nodes accept the first valid block they receive that builds upon the longest proof-of-work chain** as the next block in the chain. Occasionally, simultaneous block discoveries occur, resulting in one of those blocks being excluded from the longest chain, leading to the creation of **orphan blocks**.

When a node re-joins the network, it connects to other nodes and requests records of all transactions and blocks that have occurred since its disconnection. The nodes then validate this information and re-enter the competition from the most recently discovered block, ensuring that the **network remains fluid and adaptable to changes in participation.**


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