ZIP: 155 Title: addrv2 message Owners: Daira Hopwood <firstname.lastname@example.org> Credits: Wladimir J. van der Laan Zancas Wilcox Status: Proposed Category: Network Created: 2021-08-13 License: BSD-2-Clause Discussions-To: <https://github.com/zcash/zips/issues/542> Pull-Request: <https://github.com/zcash/zips/pull/543>
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" 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. 4
The terms "Testnet" and "Mainnet" are to be interpreted as described in section 3.11 of the Zcash Protocol Specification 2.
"P2P network" means the Zcash peer-to-peer network.
uint32 denote unsigned integer data types of the corresponding length (8, 16, or 32 bits respectively).
This document proposes a new P2P message to gossip longer node addresses over the P2P network. This is required to support new-generation onion addresses, I2P, and potentially other networks that have longer endpoint addresses than fit in the 128 bits of the current
Tor v3 onion services are part of the stable release of Tor since version 0.3.2.9. They have various advantages compared to the old v2 onion services, among which better encryption and privacy 9. These services have 256-bit addresses and thus do not fit in the existing
addr message (unchanged from Bitcoin 7), which encapsulates onion addresses in OnionCat IPv6 addresses.
Other transport-layer protocols such as I2P have always used longer addresses. This change would make it possible to gossip such addresses over the P2P network, so that other peers can connect to them.
addrv2 message is defined as a message where the
command field is (NUL-padded)
"addrv2". It is serialized in the standard encoding for P2P messages. Its format is similar to the current
addr message format described in 7, with the difference that the fixed 16-byte IP address is replaced by a network ID and a variable-length address, and the services format has been changed to 8.
This means that the message contains a serialized vector of the following structure:
Bytes Name Data Type Description 4
Time that this node was last seen as connected to the network. A time in Unix epoch time format.
Service bits. A CompactSize-encoded bit field that is 64 bits wide. 1
Network identifier. An 8-bit value that specifies which network is addressed.
The length in bytes of
Network address. The interpretation depends on networkID. 2
Network port. If not relevant for the network this MUST be 0.
One message can contain up to 1,000 addresses. Clients MUST reject messages with more addresses.
addr has a variable length, with a maximum of 512 bytes (4096 bits). Clients MUST reject messages with a longer
addr field, irrespective of the network ID.
The list of reserved network IDs is as follows:
Network ID Enumeration Address length (bytes) Description
4 IPv4 address (globally routed internet)
16 IPv6 address (globally routed internet)
32 Tor v3 onion service address
32 I2P overlay network address
16 Cjdns overlay network address
0x03 is intentionally not assigned. In BIP 155 3 it was assigned to Tor v2 onion addresses, but those addresses are no longer supported by the latest Tor client code, and MUST NOT be used once this ZIP is deployed.
Clients SHOULD gossip valid, potentially routable addresses from all known networks, even if they are currently not connected to some of them. That could help multi-homed nodes and make it more difficult for an observer to tell which networks a node is connected to.
Clients MUST NOT gossip addresses from unknown networks, because they have no means to validate those addresses and so can be tricked to gossip invalid addresses.
Clients MUST reject messages that contain addresses that have a different length than specified in this table for a specific network ID, as these are meaningless.
IPV6 network IDs use addresses encoded in the usual way for binary IPv4 and IPv6 addresses in network byte order (big endian).
According to the spec 9, version 3
.onion addresses are encoded as follows:
onion_address = base32(PUBKEY || CHECKSUM || VERSION) + ".onion" CHECKSUM = H(".onion checksum" || PUBKEY || VERSION)[:2] // first 2 bytes
PUBKEYis the 32-byte Ed25519 master pubkey of the onion service;
VERSIONis a one-byte version field (default value
".onion checksum"are constant strings;
CHECKSUMis truncated to two bytes before inserting it in
H()is the SHA3-256 cryptographic hash function. 10
Tor v3 addresses MUST be sent with the
TORV3 network ID, with the 32-byte
PUBKEY part in the
addr field. As
VERSION will always be 0x03 in the case of v3 addresses, this is enough to reconstruct the onion address.
Like Tor, I2P naming uses a base32-encoded address format 11.
I2P uses 52 characters (256 bits) to represent the full SHA-256 hash, followed by
.b32.i2p. The base32 encoding does not include
"=" padding characters.
I2P addresses MUST be sent with the
I2P network ID, with the decoded SHA-256 hash as address field.
Cjdns addresses are simply IPv6 addresses in the
fc00::/8 range 12. They MUST be sent with the
CJDNS network ID. They are encoded in network byte order (big endian) as for the
IPV6 network ID.
Support for this specification is signalled by peer protocol version 170015 (on both Testnet and Mainnet). Note that this is the same peer protocol version that signals support for NU5 on Mainnet 6.
Nodes that have not negotiated peer protocol version 170015 or higher on a given connection, MUST NOT send
addrv2 messages on that connection.
A node that has negotiated peer protocol version 170015 or higher on a given connection, MAY still send
addr messages on the connection, and MUST handle received
addr messages as it would have done prior to this ZIP.
This ZIP is closely based on BIP 155 3, with the following changes:
addrv2message is signalled by advertising a peer protocol version of 170015 or higher, not by sending a
sendaddrv2message. This is motivated by a desire to avoid an exponential explosion in the space of possible feature configurations in a given peer-to-peer connection. In Zcash, unlike Bitcoin, the space of such configurations is effectively constant no matter how many peer-to-peer protocol changes are made, because nodes that do not support a given peer protocol version will drop off the network over time if they do not support the latest Network Upgrade. The feature configuration for a given connection is also established at version negotiation, and cannot change after that point without reconnecting. Other peer-to-peer protocol changes ported from the Bitcoin peer-to-peer protocol, for example the
MSG_WTXinv type defined in ZIP 239 5, have taken the same approach to signalling.
addrv2messages with more than 1,000 addresses. Making this a consistent requirement promotes interoperability.
This ZIP is closely based on BIP 155 3, written by Wladimir J. van der Laan. Zancas Wilcox ported the implementation for Zcashd.
Acknowledgements for BIP 155:
CompactSize, to make the message more compact in the likely case instead of always using 8 bytes.
|1||RFC 2119: Key words for use in RFCs to Indicate Requirement Levels|
|2||Zcash Protocol Specification, Version 2020.2.14 [NU5 proposal]. Section 3.12 Mainnet and Testnet|
|3||BIP 155: addrv2 message|
|4||ZIP 200: Network Upgrade Mechanism|
|5||ZIP 239: Relay of Version 5 Transactions|
|6||ZIP 252: Deployment of the NU5 Network Upgrade|
|7||Protocol documentation: addr. Bitcoin Wiki|
|8||Variable length integer. Bitcoin Wiki|
|9||Tor Rendezvous Specification - Version 3|
|10||NIST FIPS 202 - SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions|
|11||I2P: Naming and address book|
|12||Cjdns whitepaper: Pulling It All Together|