What is the difference between Flooding and Broadcasting?

In a network, flooding is the forwarding by a router of a packet from any node to every other node attached to the router except the node from which the packet arrived. Flooding is a way to distribute routing information updates quickly to every node in a large network. It is also sometimes used in multicast packets (from one source node to many specific nodes in a real or virtual network).

The Internet's Open Shortest Path First (OSPF) protocol, which updates router information in a network, uses flooding.

在網路環境中，Flooding(洪泛)是一種藉由路由器繞送一封包從任何結點到其他可以抵達節點的運作方式。在大型網路環境中，Flooding是一種快速分享路由資訊給予分散路由節點的技術。他們有些時候會使用群播的方式發出封包(在實體或虛擬網路中，從單一結點到一群指定結點)。

在網際網路的OSPF協定運作中，即是利用Flooding進行路由資料交換。

Flooding vs Broadcasting 
Routing is the process of choosing which paths to be used to send network traffic, and sending the packets along the selected sub-network. Flooding and Broadcast are two routing algorithms used in computer networks today. Flooding sends all incoming packets through every outgoing edge. Broadcasting means every device in the network will receive a packet.

What is Flooding?
Flooding is a very simple routing algorithm which sends all incoming packets through every outgoing edge. Because of how this routing algorithm works, a packet is guaranteed to be delivered (if it can be delivered).

What is Broadcasting?
Broadcasting is a method used in computer networking, which makes sure that every device in the network will receive a (broadcasted) packet. Because broadcasting can impact performance in a negative way, not every network technology supports broadcasting. X.25 and frame relay does not support broadcasting and there is no such thing as internet-wide broadcasting.

What is the difference between Flooding and Broadcasting?
Sending a packet to all hosts simultaneously is broadcasting. But flooding does not send packets to all hosts simultaneously. The packets would ultimately reach all nodes in the network due to flooding. Flooding may send the same packet along the same link multiple times, but broadcasting sends a packet along a link at most once. Several copies of the same packet may reach nodes in flooding, while broadcasting does not cause that problem. Unlike flooding, broadcasting is done by specifying a special broadcast address on packets.

簡單來說，Flooding的機制，會有機會在同一節點上收到兩個以上相同封包；但是Broadcasting不會發生，因為Broadcasting通常會使用一個指定的廣播位址，就是該次一次性的送出。