NU5 deployment

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

• The Zcash Protocol Specification 2 4
• ZIP 200: Network Upgrade Mechanism 6
• ZIP 216: Require Canonical Point Encodings 12
• ZIP 224: Orchard Shielded Protocol 14
• ZIP 225: Version 5 Transaction Format 15
• ZIP 239: Relay of Version 5 Transactions 16
• ZIP 244: Transaction Identifier Non-Malleability 17
• The Orchard Book 20
• The halo2 Book 21

The network handshake and peer management mechanisms defined in ZIP 201 7 also apply to this upgrade.

Unified addresses and viewing keys are described in ZIP 316 18.

The following ZIPs have been updated in varying degrees to take into account Orchard:

• ZIP 32: Shielded Hierarchical Deterministic Wallets 5
• ZIP 203: Transaction Expiry 8
• ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances 9
• ZIP 212: Allow Recipient to Derive Ephemeral Secret from Note Plaintext 10
• ZIP 213: Shielded Coinbase 11
• ZIP 221: FlyClient - Consensus-Layer Changes 13
• ZIP 401: Addressing Mempool Denial-of-Service 19

The following network upgrade constants 6 are defined for the NU5 upgrade:

CONSENSUS_BRANCH_ID

0xc2d6d0b4

ACTIVATION_HEIGHT (NU5)

Testnet (second activation): 1842420

Mainnet: 1687104

MIN_NETWORK_PROTOCOL_VERSION (NU5)

Testnet (second activation): 170050

Mainnet: 170100

Note: A first activation of NU5, with a previous version of the Orchard circuit and other NU5 consensus rules, occurred on Testnet at block height 1599200 with consensus branch ID 0x37519621 and peer protocol version 170015. With the release of zcashd v4.7.0, Testnet is being rolled back to another chain that forks from the block immediately preceding that activation, at height 1599199. This chain had been continuously mined by zcashd v4.0.0 nodes modified to disable End-of-Service halt.

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 the MIN_NETWORK_PROTOCOL_VERSION (NU5) for that activation.

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 took effect from peer protocol version 170014 onward, on both Testnet and Mainnet. 16

Backward compatibility in zcashd

The minimum peer protocol version that NU5-compatible zcashd nodes will connect to is 170002. On Testnet, they will immediately disconnect from nodes advertising a peer protocol version less than 170040.

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 7.

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. They will immediately disconnect from nodes advertising a peer protocol version less than:

• 170040 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 existing connections with pre-NU5 peers, and reject new connections from pre-NU5 peers.