The Bitcoin Cash Peer-to-Peer (P2P) Network protocol is a binary protocol used by Full Nodes and [SPV](/protocol/simple-payment-verification) Nodes, transmitted over TCP/IP.
Individual nodes on the Bitcoin Cash network connect and create a mesh network where each node is indirectly connected to many others via just a couple of hops.
In the original Satoshi implementation of the P2P protocol the design of INV and getdata have been used for propagating transaction data using the rules of the gossip protocol values: forwarding validated transactions to a few peer-nodes who send it to others until the entire network has the transaction.
This emergent behavior of the P2P layer allows fast propagation without undue strain on any individual node.
*Developer Notes: A common message strategy is to wait for any message that provides the required data (with a timeout), and then separately issue the request in a retry loop to multiple peers.*
| payload byte count | 4 bytes | unsigned integer<sup>[(LE)](/protocol/misc/endian/little)</sup> | The size of the payload. The total max size of any message is `268,435,456` bytes (256 MiB), and the header for a message is always 24 bytes, therefore the max value of the payload byte count is `268,435,432` bytes, while the min value is zero (indicating no additional payload). |
| payload checksum | 4 bytes | byte array<sup>[(BE)](/protocol/misc/endian/big)</sup> | The message checksum is the first 4 bytes of a double-sha256 hash of the payload. |
| payload | variable | message-specific | See [message types](#message-types) for links to message-specific page, which describe the payload for each message. |
The network identifier is used to separate blockchains and test networks.
This reduces unnecessary load on peers, allowing them to rapidly ban nodes rather then forcing the peer to do a blockchain analysis before banning or disconnecting.
The `net magic` is designed to be unlikely to occur in normal data--the characters are rarely used upper ASCII, are not valid as UTF-8, and produce a large 32-bit integer with any alignment.
Messages with an unrecognized `command string` are ignored by most implementations but may result in a ban by implementations that diverge from the Satoshi-client defacto standard.
Compact blocks, defined in [BIP-152](/protocol/forks/bip-0152), seek to minimize the amount of data transferred when a block is mined by taking advantage of the fact that peers often already have most, if not all, of the transactions in a new block.
| Command String | Synopsis |
| -- | -- |
| [sendcmpct](/protocol/network/messages/sendcmpct) | *Indicates that this node supports the Compact Block protocol.* |
| [cmpctblock](/protocol/network/messages/cmpctblock) | *Announces and provides abbreviated contents of a block.* |
| [getblocktxn](/protocol/network/messages/getblocktxn) | *Requests additional transactions from a given block.* |
| [blocktxn](/protocol/network/messages/blocktxn) | *Returns requests transactions contained within a block (in response to [getblocktxn](/protocol/network/messages/getblocktxn).* |
