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<div class="cwikmeta">{
"title":"INV",
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"related":["/protocol","/protocol/network/messages/getdata.md","/protocol/network/messages/filterload.md","/protocol/network/messages/filterclear.md"]
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}</div>
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* Notifies peers about the existence of some information (block or transaction) *
Based on selected services in the [VERSION ](/protocol/network/messages/version.md ) message, INV messages may not be sent.
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If a bloom filter has been sent to this node via [FILTERLOAD ](/protocol/network/messages/filterload.md ), transaction INVs will only be sent if they match the bloom filter.
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| compact int | 4 bytes | 32 bytes |... | 4 bytes | 32 bytes |
|----------|---------|----------|---|---------|----------|
|[vector ](/protocol/p2p/vector.md ) size N of| type 1 | hash 1 | | type N | hash N
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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.
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##### Type
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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 )
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##### Hash
The [hash identifier ](/glossary/hash__identifier.md ) of the available object.
