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Handshake: Version (“version”)

The version message is a part of the node connection handshake and indicates various connection settings, networking information, and the services provided by the sending node (see Services Bitfield below).

The node connection is not considered established until both nodes have sent and received both a version and verack message.

Message Format

Field Length Format Description
version number 4 bytes unsigned integer(LE) The version number supported by the sending node.
services 8 bytes bitfield(LE) An indication of the services supported by the sending node. See Services Bitfield section below.
timestamp 8 bytes unix timestamp(LE) The time the message was generated on the sending node.
remote address 26 bytes network address The network address of the remote node.

NOTE: this does not contain the timestamp normally included with network addresses.
local address 26 bytes network address The network address of the sending node.

NOTE: this does not contain the timestamp normally included with network addresses.
nonce 8 bytes bytes(LE) Random nonce for the connection, used to detect connections to self.
user agent variable variable length string A user agent string identifying the node implementation.
block height 4 bytes unsigned integer(LE) The height of the block with the highest height known to the sending node.
relay flag 1 byte boolean Indicates whether the sending node would like all broadcasted transactions relayed to it. See BIP-37. This flag is sometimes referred to as "fRelay".

Note: Protocol version 70001 introduced the optional relay flag. Transmitting the relay flag byte to Nodes with a version less than 70001 may result in incompatibility with versions that validate the Version message for a specific byte count.

Note: Historically, transmitting extra data after the relay flag would result in the connection being banned by some Nodes. Modern Nodes ignore extra data after the relay flag.

Version Number

The most recent version of the network protocol is 70015. The version value often correlates to new behavior, parsing formats, and available services; for more details review the network protocol's version history. Nodes should use version and the services bitfield to determine if the node should accept the incoming connection.

Related: node connection handshake.

Services Bitfield

The services field is an 8 byte little-endian-serialized bitfield that described peer capabilities. The benefit of this bitfield is that during the handshake a node learns about the services his peer offers. Nodes may selectively disconnect from nodes that do not supported "desired services".

When a service is advertised, a separate handshake may follow with service-specific messages to learn details about the support a peer has for that specific service.

The following capabilities are defined, by bit position:

Standard Services

  • 0: NODE_NETWORK The node is capable of serving the complete block chain. It is currently set by all full nodes, and is unset by SPV clients or other peers that just want network services but don't provide them.

  • 2: NODE_BLOOM The node is capable and willing to handle bloom-filtered connections.

  • 4: NODE_XTHIN The node supports Xtreme Thinblocks

  • 6: NODE_GRAPHENE The node supports Graphene blocks. If this is turned off then the node will not service graphene requests nor make graphene requests.

  • 7: NODE_WEAKBLOCKS The node supports Storm weak block (currently no node supports these in production, so this is a placeholder).

  • 10: NODE_NETWORK_LIMITED This means the same as NODE_NETWORK with the limitation of only serving a small subset of the blockchain. See BIP159 for details on how this is implemented.

  • 24-31: Reserved for experimental changes These bits are reserved for temporary experiments. Just pick a bit that isn't getting used, or one not being used much, and notify the community. Remember that service bits are just unauthenticated advertisements, so implementations must be robust against collisions and other cases where nodes may be advertising a service they do not actually support.

Example Serialized Data

Net Magic(BE) 72271221

Command String ("version")(BE) 76657273696F6E0000000000

Payload Byte Count(LE) 6A000000

Payload Checksum(LE) 8FC7709F

Version Number 7F110100

Node Features 3500000000000000

Timestamp ("1576101548") AC66F15D00000000

Remote Address ("5.6.7.8:8333") 240000000000000000000000000000000000FFFF0506070820

Local Address ("1.2.3.4:8333") 8D350000000000000000000000000000000000FFFF01020304

Nonce 208D00F0E6495B9B

User Agent ("/Bitcoin Node:1.2.3/") 4350142F426974636F696E204E6F64653A312E322E332F

Current Block Height ("612918L") 365A0900

Relay Transactions Flag ("true") 01

Other Proposed/Previously Used Service Flags

  • 1: NODE_GETUTXO The node is capable of responding to the getutxo protocol request. See BIP 64 for details on how this is implemented. Was previously supported by Bitcoin XT only.

  • 8: NODE_CF Indicates the node is capable of serving compact block filters to SPV clients, AKA the "Neutrino" protocol (BIP157, and BIP158).