Protocols, Routing Protocols, Routed Protocols

In a single sentence protocol is a set of rules. Protocol governs data communication to occur. It defines the format and the order of message exchanged between two or more communication entities, as well as the actions taken on the transmission and/or receipt of a message or other event. A protocol defines what is communicated, how it is communicated, and when it is communicated. Without protocol two computer can be connected but not communicate. It is essential to use same protocol for communication between two devices. When several protocols work at a time it is called protocol suit. At present three widely used protocol suits are TCP/IP, IPX/SPX and AppleTalk.

Routing Protocols
A routing protocol sends and receives routing information packets to and from other routers. Routing protocols implement algorithms that tell routers the best paths through inter-networks. Routing protocols include Border Gateway Protocol (BGP), Interior Gateway Routing Protocol (IGRP), Routing Information Protocol, and Open Shortest Path First (OSPF) to name a few. Routing protocols provide the layer 3 network state update.

Routed Protocols
A routed protocol can be routed by a router, which means that it can be forwarded from one router to another. Such as Internet Protocol (IP), Novell Inter-network Packet eXchange (IPX), and AppleTalk are  routed protocols.

In short, routing protocols route datagrams through a network. Routing is a layer 3 function, thus, routing and routed protocols are network-layer entities. Routing tables on the layer 3 switch (router) are populated by information from routing protocols. A routed protocol will enter an interface on a router, be placed in a memory buffer, then it will be forwarded out to an interface based on information in the routing table.

Routed versus Routing Protocols
Confusion often arises between routing protocols and routed protocols. While routing protocols help the router in the decision-making on which paths to send traffic, routed protocols are responsible for the actual transfer of traffic between Layer3 devices. Specifically, a routed protocol is any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme, without knowing the entire path from source to destination. Routed protocols define the format and use of the fields within a packet. Packets generally are conveyed from end system to end system.


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