NU5 deployment

The primary sources of information about NU5 consensus and peer-to-peer protocol changes are:

• The Zcash Protocol Specification 2
• ZIP 200: Network Upgrade Mechanism 7
• ZIP 216: Require Canonical Point Encodings 9
• ZIP 221: FlyClient - Consensus-Layer Changes 10 (amended)
• ZIP 224: Orchard Shielded Protocol 11
• ZIP 225: Version 5 Transaction Format 12
• ZIP 239: Relay of Version 5 Transactions 13
• ZIP 244: Transaction Identifier Non-Malleability 14
• The Orchard Book 16
• The halo2 Book 17

The network handshake and peer management mechanisms defined in ZIP 201 8 also apply to this upgrade. Unified addresses and viewing keys are described in ZIP 316 15. ZIP 32 5 has been amended to include hierarchical key derivation for Orchard.

Support for the addrv2 peer protocol message, defined in ZIP 155 [#zip-0155], is being added concurrently with this upgrade, signalled by the same Mainnet peer protocol version.

The following network upgrade constants 7 are defined for the NU5 upgrade:

CONSENSUS_BRANCH_ID

0xF919A198

ACTIVATION_HEIGHT (NU5)

Testnet: TODO

Mainnet: TODO

MIN_NETWORK_PROTOCOL_VERSION (NU5)

Testnet: 170014

Mainnet: 170015

For each network (Testnet and Mainnet), nodes compatible with NU5 activation on that network MUST advertise a network protocol version that is greater than or equal to that network's MIN_NETWORK_PROTOCOL_VERSION (NU5).

For each network, pre-NU5 nodes are defined as nodes advertising a protocol version less than that network's MIN_NETWORK_PROTOCOL_VERSION (NU5).

Once NU5 activates on Testnet or Mainnet, NU5 nodes SHOULD take steps to:

• reject new connections from pre-NU5 nodes on that network;
• disconnect any existing connections to pre-NU5 nodes on that network.

The change to the peer-to-peer protocol described in ZIP 239 takes effect from peer protocol version 170014 onward, on both Testnet and Mainnet. 13

The change to the peer-to-peer protocol described in ZIP 155 takes effect from peer protocol version 170015 onward, on both Testnet and Mainnet. 6

Note: these peer-to-peer protocol changes are enabled whenever the relevant version (or higher) is negotiated on a given connection, which can happen in advance of the Testnet or Mainnet NU5 activation.

Backward compatibility in zcashd

The minimum peer protocol version that NU5-compatible zcashd nodes will connect to is 170002.

NU5 deployment for zcashd

For each network, approximately 1.5 days (defined in terms of block height) before the corresponding NU5 activation height, nodes compatible with NU5 activation on that network will change the behaviour of their peer connection logic in order to prefer pre-NU5 peers on that network for eviction from the set of peer connections:

/**
 * The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks).
 * This was three days for upgrades up to and including Blossom, and is 1.5 days from Heartwood onward.
 */
static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 1728;

The implementation is similar to that for Overwinter which was described in 8.

However, NU5 nodes will have a preference for connecting to other NU5 nodes, so pre-NU5 nodes will gradually be disconnected in the run up to activation.

Backward compatibility in Zebra

The minimum peer protocol version that NU5-compatible Zebra nodes will connect to is 170002. However, Zebra will immediately disconnect from nodes with a protocol version less than:

• 170012 on Testnet, or
• 170013 on Mainnet.

NU5 deployment for Zebra

For each network, at the corresponding NU5 activation height, nodes compatible with NU5 activation on that network will close any new connections with pre-NU5 peers.

Since Zebra maintains a reasonably strict internal request-response protocol, pre-NU5 nodes will gradually be disconnected after activation. (Nodes are temporarily disconnected if they send gossip or chain sync hints outside the strict request-response sequence that Zebra expects.)