Broadcasting Transactions to the Network

• •Definition: Sending your signed transaction to Bitcoin nodes on the network.
• •Peer-to-peer: No central server—transactions spread node-to-node.
• •Validation: Each node checks the transaction is valid before relaying.
• •Speed: Propagates to most of the network within seconds.
• •Irreversible: Once broadcast, you can't un-send (but can try to replace with RBF).

• •Broadcasting: Sending a transaction to the network.
• •Peer-to-peer (P2P): Network structure where nodes connect directly without central server.
• •Node: A computer running Bitcoin software that validates and relays transactions.
• •Relay: Passing a transaction to connected peers.
• •Propagation: The process of a transaction spreading across the network.
• •Mempool: Memory pool where unconfirmed transactions wait for confirmation.

Timeline:

• •0 seconds: You broadcast to 1-8 connected nodes
• •1-2 seconds: Those nodes relay to their peers (~hundreds of nodes)
• •5-10 seconds: Reaches most of the network (~10,000+ nodes)
• •Within 30 seconds: Nearly universal propagation

Exponential spread:

• •Round 1: 8 nodes
• •Round 2: 64 nodes
• •Round 3: 512 nodes
• •Round 4: 4,096 nodes
• •Round 5: 32,768 nodes

1. Via Your Wallet

• •Most common method
• •Wallet connects to nodes and broadcasts automatically
• •Examples: Electrum connects to Electrum servers, Bitcoin Core to full node peers

2. Via Your Own Node

• •Run Bitcoin Core or similar
• •Connect wallet to your node
• •More private (don't leak addresses to third parties)
• •More reliable (you control the connection)

3. Via Public APIs/Block Explorers

• •Websites like blockchain.com, mempool.space offer broadcasting
• •Copy raw transaction hex, paste into website
• •Less private (service knows your IP and transaction)
• •Useful as backup if wallet connection fails

4. Via Tor

• •Route through Tor network for IP privacy
• •Hides your location from nodes
• •Wasabi, Samourai wallets support this
• •Slower but more private

Basic checks:

• •Valid format and syntax
• •Signatures are correct
• •Inputs reference unspent outputs
• •Inputs ≥ outputs (no negative fees)
• •Output values ≥ dust limit
• •Transaction size within limits

If invalid:

• •Node rejects and doesn't relay
• •Transaction dies (doesn't propagate)
• •Wallet might show error or just fail silently

If valid:

• •Node adds to its mempool
• •Relays to peers
• •Transaction propagates

What nodes learn:

• •Your transaction details (inputs, outputs, amounts)
• •Your IP address (if not using Tor/VPN)
• •Timing of broadcast

How to improve privacy:

• •Use your own node (don't trust third parties)
• •Route through Tor or VPN
• •Use CoinJoin before sending
• •Don't link addresses (avoid input linking)
• •Batch transactions to hide recipient count

Transaction doesn't propagate:

• •Invalid signature or format
• •Spending already-spent output
• •Fee too low (some nodes have minimum fee filters)
• •Transaction too large (>100 KB rejected by default)
• •Nonstandard transaction (unusual scripts)

Solution:

• •Check wallet error messages
• •Verify transaction is valid
• •Try broadcasting via different node/service
• •Increase fee if too low
• •Wait and retry if temporary network issue