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protocol/p2p/inv.md

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+<div class="cwikmeta">{
+"title":"INV",
+"related":["/protocol","/protocol/p2p/getdata","/protocol/p2p/filterload","/protocol/p2p/filterclear"]
+}</div>
+
+*Notifies peers about the existence of some information (block or transaction)*
+Based on selected services in the [VERSION]("/protocol/p2p/version") message, INV messages may not be sent.
+
+If a bloom filter has been sent to this node via [FILTERLOAD](/protocol/p2p/filterload), transaction INVs will only be sent if they match the bloom filter.
+
+| compact int | 4 bytes | 32 bytes |... | 4 bytes | 32 bytes |
+|----------|---------|----------|---|---------|----------| 
+|[vector](/protocol/p2p/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++](https://github.com/BitcoinUnlimited/BitcoinUnlimited/blob/eb264e627e231f7219e60eef41b4e37cc52d6d9d/src/protocol.h#L477)
+
+##### Hash
+The [hash identifier](/glossary/hash__identifier) of the available object.