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ZIP: 252
Title: Deployment of the NU5 Network Upgrade
Owners: teor <[email protected]>
        Daira Hopwood <[email protected]>
Status: Proposed
Category: Consensus / Network
Created: 2021-02-23
License: MIT
Discussions-To: <https://github.com/zcash/zips/issues/440>
Pull-Request: <https://github.com/zcash/zips/pull/446>

Terminology

The key words "MUST" and "SHOULD" in this document are to be interpreted as described in RFC 2119. [1]

The term "network upgrade" in this document is to be interpreted as described in ZIP 200. [7]

The terms "Testnet" and "Mainnet" are to be interpreted as described in section 3.11 of the Zcash Protocol Specification [3].

Abstract

This proposal defines the deployment of the NU5 network upgrade.

Specification

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

Prior to the network upgrade activating on each network, NU5 and pre-NU5 nodes are compatible and can connect to each other.

Once the network upgrades, even though pre-NU5 nodes can still accept the numerically larger protocol version used by NU5 as being valid, NU5 nodes will always disconnect peers using lower protocol versions.

Unlike Blossom, Heartwood, and Canopy, and like Overwinter and Sapling, NU5 defines a new transaction version. Therefore, NU5 transactions MAY be in the new v5 format specified by [12]. Unlike previous transaction version updates, the existing v4 transaction format remains valid after NU5 activation. Both transaction formats MUST be accepted by NU5 nodes.

Backward compatibility of the new MSG_WTX inv type introduced for inv and getdata messages is discussed in [13].

Backward compatibility of the new addrv2 message (not technically part of NU5) is discussed in [6].

Support in zcashd

TODO: Update as needed

Support for NU5 on Testnet will be implemented in zcashd version 4.5.0, which will advertise protocol version 170014. Support for NU5 on Mainnet will be implemented in zcashd version 5.0.0, which will advertise protocol version 170015.

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.

Support in Zebra

TODO: Update as needed

Support for NU5 on Testnet will be implemented in Zebra version 1.0.0, which will advertise protocol version 170014. Support for NU5 on Mainnet will be implemented in Zebra version 2.0.0, which will advertise protocol version 170015.

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.)

References

[1]RFC 2119: Key words for use in RFCs to Indicate Requirement Levels
[2]Zcash Protocol Specification, Version 2021.1.24 or later
[3]Zcash Protocol Specification, Version 2021.1.24 [NU5 proposal]. Section 3.11: Mainnet and Testnet
[4]Zcash Protocol Specification, Version 2021.1.24 [NU5 proposal]. Section 7.1: Transaction Encoding and Consensus
[5]ZIP 32: Shielded Hierarchical Deterministic Wallets
[6](1, 2) ZIP 155: addrv2 message
[7](1, 2, 3) ZIP 200: Network Upgrade Mechanism
[8](1, 2) ZIP 201: Network Peer Management for Overwinter
[9]ZIP 216: Require Canonical Point Encodings
[10]ZIP 221: FlyClient - Consensus-Layer Changes
[11]ZIP 224: Orchard Shielded Protocol
[12](1, 2) ZIP 225: Version 5 Transaction Format
[13](1, 2, 3) ZIP 239: Relay of Version 5 Transactions
[14]ZIP 244: Transaction Identifier Non-Malleability
[15]ZIP 316: Unified Addresses and Unified Viewing Keys
[16]The Orchard Book
[17]The halo2 Book