This tutorial describes the differences between routed or routable protocols and routing protocols. Learn how computer networks use routing protocols and routable protocols.
The entire communication process between two devices on a computer network is mainly divided into two parts. The source device and the destination device control and manage the first part while the intermediate devices that provide connectivity between the source device and the destination device control and manage the second part.
To control and manage the communication process, the source device and the destination device use a routed protocol whereas the intermediate devices use a routing protocol. Let’s take a simple example.
Suppose, two devices: A and B are connected through two devices: C and D. In this case, A and B will use a routed protocol, and C and D will use a routing protocol.
The source device uses a routed protocol to pack data packets for transportation. The destination device uses the same routed protocol to unpack the received data packets from the source device.
On computer networks, routers work as intermediate devices. They connect different networks. They use routing protocols to discover all available routes and find the shortest and the fastest route between the source device and the destination device from all available routes.
Let’s take another example. In a network two PCs: PC0 and PC1 are connected through three routes: route-a, route-b, and route-c. PC0 wants to send a large data file to PC1. The routed protocol running on PC0 performs all necessary tasks that are required to send the file to PC1. These tasks include breaking the file into smaller pieces so each piece can travel over any type of route available in the network and adding the source address, the destination address, the sequence number, and other parameters to each piece.
Breaking a large file into smaller pieces is known as segmentation. The process of adding necessary information to each piece is known as encapsulation. The routed protocol performs segmentation and encapsulation on the source device. After performing all necessary tasks, the routed protocol running on the source device decides the method that it can use to send the packet to the destination device.
A source device can send a packet to the destination device by using one of two methods. These methods are sending the packet to the destination device directly and sending the packet to the destination device via the default gateway router. If the destination device is available in the local network, the source device uses the first method. If the destination device is available in the remote network, the source device uses the second method.
To learn more about these methods, you can check the following tutorial.
Basic of IP Routing Explained with Example
This tutorial step-by-step explains how the packet moves between the source device and the destination device.
If the destination device is available in the remote network, the source device gives the data packet to the default gateway router. The default gateway router reads the destination address of the packet and forwards the packet to the destination address or to the router that is connected to the destination address.
If the default gateway router knows multiple routes for the same route, it uses the shortest and the fastest route to forward the packet. To learn all available routes and calculate the shortest and the fastest route to the destination, the default gateway router, and other intermediate routers use a routing protocol.
The Destination device uses the same routed protocol to reproduce the original file from the received data packets. In our example, the routed protocol running on PC1 recreates the original file from the received data packets.
The source device and the destination device use the same routed protocol to encapsulate and de-encapsulate the data packets. The routers that connect the source device to the destination device use the same routing protocol to learn all available routes and select the best route between the source device and the destination device.
TCP/IP network
On a TCP/IP network, the source device and the destination device use the IP protocol to encapsulate and de-encapsulate the data packets. In other words, the IP protocol is the only available routed protocol on a TCP/IP network.
On a TCP/IP network, many routing protocols are available. RIP, EIGRP, and OSPF are some of the most common and widely used routing protocols. Each routing protocol uses a different technique and algorithm to find all available routes and calculate the best route from all available routes. An administrator can select a routing protocol that suites the network requirement.
Differences between routed protocols and routing protocols
The main differences between routed protocols and routing protocols are the following.
Routed protocols
- End devices use routed protocols to send and receive data packets.
- Routed protocols provide addressing to end devices.
- Routed protocols encapsulate and de-encapsulate data packets.
- If the destination address is not available in the local network, the routed protocol forwards the packet to the default gateway.
- A routed protocol does not care which route the packet takes to reach the remote destination from the default gateway.
- The IP protocol is an example of a routed protocol.
Routing protocols
- Intermediate routers use routing protocols to discover routes and calculate the best route between a source and the destination.
- Routing protocols store discovered routes in routing tables.
- Routing protocols continuously update and manage routing tables.
- Routing protocols exchange information between routers.
- Routing protocols do not care what is inside a packet. They only care about how to deliver the packet to the correct destination.
- RIP, IGRP, EIGRP, OSPF, IS-IS are some examples of routing protocols.
How routed and routing protocols work on a computer network
Let’s take another example to understand how a computer network uses routed and routing protocols.
The following image shows the layout of a network. In this network, PC0 and PC1 are connected to PC2 via four routers; R1, R2, R3, and R4.
Suppose, an application running on PC0 wants to send some data to PC1. The application calls the IP protocol of PC0 and hands that data over to the IP protocol. The IP protocol packs data into packets and adds source address and destination address to each packet.
If the destination address is located in the same IP subnet, the IP protocol sends packets directly to the destination host.
The entire routing process is controlled by the routed (IP) protocols of PC0 and PC1.
Now suppose, the same application wants to send data to PC2. The same process is repeated until the packet forwarding decision is made by the IP protocol. This time, since the destination host (PC2) is located in a different IP subnet, the IP protocol sends packets to the default gateway router.
The default gateway router not only keeps records of all remote networks but also keeps records of all available paths for each remote network. A router maintains these records in the routing table. A typical routing table entry consists of two pieces; the network address and the interface on which that network is available.
When a router receives a packet on any of its interfaces, it reads the destination network of the packet and finds the destination network in the routing table. If the routing table contains a record for the destination network, the router uses the record to forward the packet. If the routing table doesn’t contain a record for the destination network, the router discards the packet.
If multiple paths to a remote network exist, the router chooses the fastest path.
In our example, the default gateway router R1 has two paths to reach PC2's network. When it receives packets for PC2 from PC0, it compares both paths and chooses the fastest path to forward packets. For this, R1 uses the routing protocol. Routing protocols help routers to find all paths and select the best path for each destination.
PC2 receives packets from its default gateway router R4. Routed (IP) protocol running on PC2 processes the received packets.
That’s all for this tutorial. In this tutorial, we discussed the routed and routing protocols and learned about the differences between them. In the next tutorial, we will learn the types of routing protocols.
