Flooding is a simple routing/forwarding technique in which every router, on receiving a packet, sends a copy of it out on every outgoing line except the one on which it arrived.

• The packet spreads through the entire network like a wave, so if any path exists between source and destination, the packet is guaranteed to be delivered — it is highly robust against link/router failures.
• To stop infinite circulation, a hop counter (sequence number) is decremented at each hop, and duplicate packets are discarded by remembering (packet id, port).
• Drawbacks: heavy traffic congestion and duplicate packets; used mainly for broadcast, for broadcasting management/trap messages, or as a fallback during network failures.