# # Chain ID

Learn about the Haqq chain-id format

## # The Chain Identifier

Every chain must have a unique identifier or chain-id. Tendermint requires each application to define its own chain-id in the genesis.json fields (opens new window). However, in order to comply with both EIP155 and Cosmos standard for chain upgrades, Haqq-compatible chains must implement a special structure for their chain identifiers.

## # Structure

The Haqq Chain ID contains 3 main components

• Identifier: Unstructured string that defines the name of the application.
• EIP155 Number: Immutable EIP155 (opens new window) CHAIN_ID that defines the replay attack protection number.
• Version Number: Is the version number (always positive) that the chain is currently running. This number MUST be incremented every time the chain is upgraded or forked in order to avoid network or consensus errors.

### # Format

The format for specifying and Haqq compatible chain-id in genesis is the following:

Copy {identifier}_{EIP155}-{version}

The following table provides an example where the second row corresponds to an upgrade from the first one:

ChainID Identifier EIP155 Number Version Number
haqq_11235-1 haqq 11235 1
haqq_11235-2 haqq 11235 2
... ... ... ...
haqq_11235-N haqq 11235 N