Node discovery, channel discovery, and channel updates are broadcasted through gossip messages on the Lightning network. Rather than relying on a third-party to distribute information, Lightning relies on announcements containing information with network updates.
To support channel discovery, three gossip messages are supported. Peers in the network exchange
channel_announcement messages containing information regarding new channels between the two nodes. They can also exchange
channel_update messages, which update information about a channel. There can only be one valid
channel_announcement for any channel, but at least two
channel_update messages are expected.
To support node discovery, peers exchange
node_announcement messages, which supply additional information about the nodes. There may be multiple
node_announcement messages, in order to update the node information.