Networking

All P2P communication goes through libp2p. Transport stack: TCP → Noise XX (encrypted, mutual auth) → Yamux (multiplexed streams).

Transport

// transport.rs — simplified
tcp::Config::default().nodelay(true)  // low latency
→ noise::Config::new                  // Noise XX handshake
→ yamux::Config::default              // stream multiplexing

Noise XX gives mutual authentication (both sides prove identity via Ed25519 keypair) and forward secrecy. No certificates needed.

Node Identity

Each node has an Ed25519 keypair at data/identity/node_keypair, generated on first run. PeerId = hash of public key. Stays the same across restarts even if IP changes.

Peer Discovery

Two mechanisms:

1. Kademlia DHT — automatic peer discovery via random walks every 60s. When Identify completes, peer listen addresses are added to the Kademlia routing table. New nodes discover the network by connecting to one bootstrap peer.
2. Manual — pass --peers on startup as fallback:

SENTRIX_VALIDATOR_KEY=<key> sentrix start --peers [NODE_IP]:30303,[NODE_IP]:30303

Peers go through chain_id verification before being added to verified_peers. Wrong chain_id = disconnected immediately.

Bootstrap peers re-dialed every 30s if disconnected. Idle timeout set to Duration::MAX — connections stay open permanently.

Kademlia protocol: /sentrix/kad/1.0.0 with in-memory store.

Block & Transaction Propagation (Gossipsub)

Blocks and transactions propagate via gossipsub pub/sub:

Topic	Content	Format
sentrix/blocks/1	New blocks	bincode-encoded GossipBlock
sentrix/txs/1	New transactions	bincode-encoded GossipTransaction

Gossipsub config: 5s heartbeat, strict validation, 10 MiB max message size.

When a gossipsub message arrives, the block/transaction is validated via the same add_block() / add_to_mempool() path as request-response messages.

Request-Response Messages

Length-prefixed bincode over RequestResponse protocol. 4-byte BE length header, 10 MiB cap.

Switched from JSON in v2.0.0 for ~3-5x smaller messages and faster serialization.

Message	What it does
NewBlock	Broadcast new block to all peers
NewTransaction	Propagate new tx
GetBlocks	Request blocks from a height range
BlocksResponse	Return up to 50 blocks
Handshake	Chain ID check on connect

Sync

Every 30 seconds, check if any peer is ahead. If yes:

1. Request blocks from local_height + 1 in batches of 50
2. Validate each block via add_block() (same two-pass as locally produced blocks)
3. Save to MDBX immediately after each accepted block
4. Repeat until caught up

Sync and block processing run in tokio::spawn() tasks — they don't block the swarm event loop.

Rate Limiting

• Max 5 connections per IP per 60s
• IPs that exceed this get banned for 5 minutes
• Max 50 total peers
• Rate limiter state auto-pruned periodically

Ports

Port	Use
30303	P2P (libp2p)
8545	REST API + JSON-RPC + Explorer

Behaviour

struct SentrixBehaviour {
    identify: identify::Behaviour,
    kademlia: kad::Behaviour<kad::store::MemoryStore>,
    gossipsub: gossipsub::Behaviour,
    rr: request_response::Behaviour<SentrixCodec>,
}

• Identify: peer info exchange, feeds addresses into Kademlia
• Kademlia: DHT-based peer discovery with periodic bootstrap
• Gossipsub: pub/sub block and transaction propagation
• RequestResponse: sync, handshake, height queries (bincode codec)