Gossip and the channel graph

To find a route to Dina, Alice needs a map: which nodes exist and which channels connect them. Nobody publishes that map. Every node builds its own from gossip, messages it hears from its peers and passes on.

Three gossip messages

A channel is announced only after its funding transaction has six confirmations. That stops nodes from spamming the map with channels that don't exist: anyone can check the funding output on the blockchain.

Capacity, not balance

The graph shows each channel's capacity, the funding amount, but never how it's split between the two sides. Balances change with every payment and would reveal who paid whom. This is why senders sometimes try a route and fail: the map says the channel is big enough, but the balance on the needed side isn't.

Read Alice's map

⚡Read the channel graph

Python

NodeAlice · LNDBob · c-lightningChan · c-lightningDina · LNDNo node

from jifunze_lab import lnd graph = lnd("alice").graph() alias = {n["pub_key"]: n.get("alias") or n["pub_key"][:8] for n in graph["nodes"]} print("nodes:", len(graph["nodes"])) print("channels:", len(graph["edges"])) for edge in graph["edges"]: print(alias.get(edge["node1_pub"]), "<->", alias.get(edge["node2_pub"]), edge["capacity"], "sats")

▶ RunCheckReset lessonRestore starter code

These exercises need a laptop with the lab running. You can read the lesson on your phone.

Your counts should match the scenario: four nodes and three channels in a line. The book's lngraph.py does the same thing on the real network, where the graph holds many thousands of nodes.