Flat routing protocols are primarily those that don’t work under a predefined network layout and perimeter. They enable the delivery of packets among routers through any available path without considering network hierarchy, distribution and composition.
Flat routing protocol is implemented in flat networks where each router node routinely collects and distributes routing information with its neighboring routers. The entire participating node addressed by flat routing protocol performs an equal role in the overall routing mechanism. Routing Information Protocol, Interior Gateway Routing Protocol and Enhanced Interior Gateway Routing Protocol are popular examples of flat routing protocols.