Replay protection is a security mechanism designed to prevent unauthorized duplication of transactions across different networks or forks of a blockchain. When a blockchain splits into two, such as during a fork, users can hold assets on both chains. Without proper protection, a transaction made on one chain could be replicated on the other, leading to issues like double spending.To mitigate this risk, protocols implement replay protection by introducing unique identifiers or signatures that are valid only on one specific chain. For example, a transaction on one fork may include a nonce or a chain-specific code, making it invalid if someone tries to use it on the alternate chain.This mechanism enhances user security and supports the integrity of each network by ensuring transactions are honored only within their intended chain. Overall, replay protection is crucial for maintaining trust and stability in blockchain systems, especially during periods of significant changes like forks.