What changed in Bitcoin P2P protocol version 70017 compared to 70016?

External question — Bitcoin Stack Exchange Author: deyw Original post: https://bitcoin.stackexchange.com/questions/131080 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I recently installed Bitcoin Core 32.0rc2 on one of my nodes and noticed that the reported P2P protocol version changed from 70016 to 70017. I remember 70016 being used for quite a long time, so I was curious what exactly triggered the protocol version bump. What changed in protocol version 70017 compared to 70016? Also, how does a 70017 node behave when connected to a peer that only supports 70016?

External answer — Bitcoin Stack Exchange Author: Ava Chow Original post: https://bitcoin.stackexchange.com/a/131081 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. BIP 434 specifies the version number 70017. The version number is incremented in order to support a new network message type that will be sent during the version handshake, at a time where the behavior regarding unknown/unexpected messages is undefined. Incrementing the version number allows peers to be certain that a node which advertises that version number is following BIP 434 and will not do anything unexpected (such as disconnecting) when it receives the new message type. BIP 434 itself is specifies a new generic message type that can be used to advertise specific features supported by the node so that nodes can negotiate future features that may be in effect for the duration of their connection.