BitcoinMachine
TERM_DEF // UPGRADES_BIPS / BIP_155_ADDRV2_SENDADDRV2
BIP 155 (ADDRV2
/ SENDADDRV2)
BIP 155 (Addrv2 / Sendaddrv2). Expanded peer-address message supporting Tor v3, I2P, and CJDNS.

This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
WHAT_BIP_155_ADDRV2_SENDADDRV2_IS
BIP 155 (Addrv2 / Sendaddrv2) — at a glance
UPGRADES
BIP 155 — "Addrv2 / Sendaddrv2" is a proposal in the Networking family, first published in 2018 with status final. Expanded peer-address message supporting Tor v3, I2P, and CJDNS. Its technical mechanism: addrv2 message with type-byte network ID + variable-length addresses. enables Tor-only and I2P-only nodes to be findable
Why it exists
DESIGN
BIP 155 (Addrv2 / Sendaddrv2) exists to solve a specific problem: support Tor v3, I2P, CJDNS addresses in P2P discovery. Without a written, numbered spec, every wallet and node implementer would interpret the requirement differently — and Bitcoin's value depends on every implementation agreeing exactly. BIP-155 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2018.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-155 addrv2 message with type-byte network ID + variable-length addresses. Adoption today: enables Tor-only and I2P-only nodes to be findable.
1. Author drafts BIP-155 against the BIP-2 template — abstract, motivation, specification, rationale. 2. The text + a reference implementation are posted on the bitcoin-dev list and as a PR to bitcoin/bips. 3. Reviewers tear it apart: ambiguities, security concerns, edge cases, interaction with prior BIPs. 4. Once stable, the BIP editor merges it; it gets a number (BIP-155) and the status "draft" or "proposed". 5. Implementations land in Bitcoin Core / wallets / other clients. For consensus changes: activation parameters chosen. 6. After deployment + adoption, BIP-155 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-155 — quick reference card
EXAMPLE
BIP number : 155 Title : Addrv2 / Sendaddrv2 Area : Networking First published: 2018 Status : final Fork class : no Motivation : support Tor v3, I2P, CJDNS addresses in P2P discovery. Mechanism : addrv2 message with type-byte network ID + variable-length addresses. Where it shows up : enables Tor-only and I2P-only nodes to be findable. Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0155.mediawiki
KEY_PROPERTIES
OPT-IN
No authority can force a BIP on anyone. Adoption depends entirely on whether the change is genuinely useful.
NUMBERED
Stable numeric reference — BIP-155 means the same thing across every wallet, miner, and node that has read this spec.
NON-CONSENSUS
BIP-155 is not a consensus rule — clients can implement it without coordinating with the network at large.
DEPLOYED
Implementations of BIP-155 are in production. The behaviour is observable on mainnet today.
COMMON_PITFALLS
Things that catch people out
PITFALLS
  • Don't confuse "draft" / "proposed" / "final" status — read the BIP header before relying on it in production.
  • The BIP number is just an editorial counter — it doesn't imply correctness or stability. Always cross-reference with the latest bitcoin/bips repo.
RELATED_CONCEPTS
Other terms from Upgrades & BIPs — click any to read its page:
Segregated Witness (SegWit, BIP 141) Taproot (BIP 341) Tapscript (BIP 342) Schnorr (BIP 340) BIP Process Soft Fork Activation MASF (Miner-Activated Soft Fork) UASF (User-Activated Soft Fork)
TERMINOLOGY_INDEX
TERMINOLOGY
BIP 155 (Addrv2 / Sendaddrv2)
Expanded peer-address message supporting Tor v3, I2P, and CJDNS.
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness-data/">witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
The 2021 upgrade introducing key-aggregable schnorr-signatures/">Schnorr signatures and Merkleized script trees.
Tapscript (BIP 342)
Script-language updates accompanying Taproot — new opcodes, removed limits.
Schnorr (BIP 340)
The Schnorr signature spec adopted by Taproot.
BIP Process
The community workflow for proposing, discussing, and tracking changes to Bitcoin.
Soft Fork Activation
The mechanism (versionbits, MASF, UASF, Speedy Trial) by which soft forks turn on.
MASF (Miner-Activated Soft Fork)
Activation triggered by miner signaling in block versions.