Gossip
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.
​BOLT #7​
[1] https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md​
