Notifies peers about the existence of some information (block or transaction) Based on selected services in the VERSION message, INV messages may not be sent.

If a bloom filter has been sent to this node via FILTERLOAD, transaction INVs will only be sent if they match the bloom filter.

compact int 4 bytes 32 bytes ... 4 bytes 32 bytes
vector size N of type 1 hash 1 type N hash N

NOTE: Since a block header is a relatively small data structure, and block propagation speed is an important network metric, a peer may send HEADER messages in place of INV messages when a block arrives.

Type

The type of the object that is available.

Type Value
1 Transaction
2 Block
3 Filtered Block (partial block with merkle proof)
4 Compact block
5 Xthin block (Bitcoin Unlimited)
6 Graphene Block (Bitcoin Unlimited)

Implementations: C++

Hash

The hash identifier of the available object.