> ## Documentation Index > Fetch the complete documentation index at: https://docs.parallaxprotocol.org/llms.txt > Use this file to discover all available pages before exploring further. # TCP Peer Discovery Parallax discovers peers with a Bitcoin-style TCP gossip model, which replaced the UDP-based `discv4` discovery of v1.x releases. Each node runs: * a **Bitcoin Core-style address manager** (`addrman`) that stores up to \~65k peer records in stochastic "new" and "tried" bucket tables, keyed by a per-node secret `nKey`; * the **`parallax-disc/1`** RLPx subprotocol, carrying a mandatory session-opening `Hello` followed by `GetPeers` / `Peers` / `YourAddr` gossip messages on top of existing TCP sessions — `Hello` must be each side's first disc message, and anything else first ends the session; * a **BIP324-style v2 handshake** that lets two nodes authenticate a TCP connection knowing only each other's `ip:port` — no persistent secp256k1 identity, no enode URL, no ENR. These three pieces are **always on** in v2.0+ builds. Operators choose their compatibility posture with a single flag. Addresses travel in BIP155 form, so the same gossip carries IPv4, IPv6 and Tor v3 onion addresses — see [Tor Integration](./tor) for how onion peers behave. ## The `--legacy-discovery` flag `--legacy-discovery` controls how much of the v1.x transport surface the node exposes. UDP discovery and legacy RLPx handshake acceptance are coupled: they share the same v1.x identity model (persistent secp256k1 key, enode URL, ENR record), so the flag drives both in lockstep. | Value | UDP discv4 | Legacy RLPx | v2 handshake | addrman | | -------------------- | ------------------------ | ------------------------------------ | ------------ | --------- | | **`auto`** (default) | responder-only | accepted + dialed for `KeyType=0x01` | always on | always on | | **`on`** | full (drives dialing) | accepted + dialed | always on | always on | | **`off`** | disabled (no UDP socket) | **refused** (listener & dialer) | always on | always on | `auto` is the transitional posture: the node answers inbound discv4 PING/FINDNODE so v1.x peers can still contact it, but the addrman is the primary dial source. Most mainnet operators will never need to change it. `on` matches pre-2.0 behaviour — `discv4.RandomNodes()` is plumbed into the dial scheduler, useful when debugging against a pure v1.x network. `off` is the v3.0 posture available as an early opt-in: no UDP socket, the listener rejects anything that isn't the v2 magic byte `0xA0`, and the dialer refuses addrman entries that carry a legacy `NodeID`. The enode URL logged at startup becomes diagnostic-only — no peer handshake consumes the persistent secp256k1 key in this mode. ## Topology examples The canonical three-role mainnet setup: ``` Node A (v1.x simulated) : no v2 discovery flags → legacy RLPx, discv4 Node B (bridge) : --legacy-discovery=auto (or on) → speaks both, addrman on Node C (v2-only) : --legacy-discovery=off → v2 handshake only, no UDP ``` Under this topology, B connects to both A (legacy RLPx) and C (v2 handshake) simultaneously on the same listener. C never peers with A directly; all A-discovered addresses reach C via `parallax-disc/1` gossip through B. ## Addrbook persistence The addrman persists to `/addrbook.rlp` on clean shutdown and reloads it on next startup. The on-disk format is versioned (v1 today); upgrades introduce a new version byte plus a migration function rather than appending fields in place. Unknown newer file versions are refused without truncation — a downgrade-then-upgrade never loses the original file. ## Operator RPC The admin namespace exposes the addrbook and dial controls: * `admin_addnode .onion:port | enode://…>` — pin a peer as `source=manual`; persists across restarts and is heavily weighted in dial selection (a 4x chance multiplier, not a strict front-of-queue guarantee). * `admin_removenode .onion:port | enode://…>` — inverse of addnode. * `admin_addrbookStatus` — read-only addrbook snapshot (total/new/tried, per-source counts). * `admin_addrbookResetKey` — regenerate `nKey` and clear the tried table. Operator-only; use after a credible `nKey` leak. * `admin_dialV2 .onion:port>` — directly dial a remote over the v2 handshake. Operator-testing entry point. Three more manage the persistent ban list (see [Peer management](./peer-management) for behaviour): * `admin_setban [bantime] [absolute]` * `admin_listbanned` * `admin_clearbanned` Corresponding `parallax-cli` subcommands are `addnode`, `removenode`, `addrbook-status`, `addrbook-resetkey`, `dialv2`, `setban`, `listbanned`, `clearbanned`. ## Deprecation timeline | Release | Default `--legacy-discovery` | What changes | | -------- | ---------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | **v2.0** | `auto` | TCP discovery ships as shown above. | | **v2.2** | `off` | Once telemetry confirms v1.x peers are \<5% of the network, the default flips. | | **v3.0** | n/a — flag removed | Legacy RLPx, ENR, enode, and `p2p/discover/v4*.go` are deleted. `parallax-disc/2` replaces the v1-schema `PeerEntry`, dropping the legacy `KeyType`/`NodeID` fields while retaining BIP155 addressing so [Tor peers](./tor) survive the removal. |