Handshake: Version (“version”)
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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 Bitmask 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 bitmask(LE) An indication of the services supported by the sending node. See Services Bitmask 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 bitmask to determine if the node should accept the incoming connection.

Related: node connection handshake.

Services Bitmask

The services field is an 8 byte little-endian-serialized bitfield that described peer capabilities.
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.

  • 3: NODE_WITNESS
    Indicates that a node can be asked for blocks and transactions including witness data.
    Bitcoin Cash nodes do not have witness data so this flag should be ignored on receipt and set to 0 when sent

  • 5: NODE_BITCOIN_CASH
    The node supports the BCH chain.
    This is intended to be just a temporary service bit until the BTC/BCH fork actually happens.

  • 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)
E3E1F3E8

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

Node Specific Messages

Bitcoin ABC

  • 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.

Bitcoin Unlimited

  • 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.

  • 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.

Bitcoin Verde

  • 7: BLOCKCHAIN_INDEX_ENABLED
    Indicates that the node is an indexing node and supports returning information custom to the requesting user’s addresses.

  • 8: SLP_INDEX_ENABLED
    Indicates that the node tracks Simple Ledger Protocol validity and supports returning this status for individual transactions.

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.

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

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

Node-Specific Behavior

Generally, though node implementations may be aware of services they do not provide, they generally ignore those they don’t supported.
Any notable deviations from that behavior are documented below.

Bitcoin ABC

Bitcoin ABC nodes may, once they have reached their maximum number of peers, selectively disconnect from nodes that do not supported “desired services”, though it appears currently this just NODE_NETWORK and/or NODE_NETWORK_LIMITED.
That is, it may prefer nodes that store and serve blocks.

Bitcoin Verde

Bitcoin Verde nodes ignore any data after the relay flag field.