Routing Protocols | Routing Basic Concept | Networking Fundamentals


Routing protocol is very helpful to identify routing issue on any network. in order to learn world around them routers use the routing protocols.These are special protocols routers use to speak each other in order to share information it might have. This is how a router one side of the planet can eventually learn about the best path to a network on the other side of the planet. In this article we will learn the basics of routing protocols.

Routing Protocols | The basic concept of Routing

There are two main category of routing_protocols. They are: Interior Gateway Protocols, and Exterior Gateway Protocols. Interior Gateway Protocols further split into two main categories. They are: Link State Routing Protocols, and Distance-Vector Protocols.

Interior Gateway Protocols

The interior gateway protocols routers use to share information within a single Autonomous System. In networking term an Autonomous System is a collection of networks that all fall under the control of single network operator. The best example of this would be a large corporation that need to route data between their many offices. Also each if those offices might have their own Local Network. Another example of this would be an ISP who employees many routers.

The two main type of Interior Gateway Protocols are: Link State Protocols, and Distance Vector Protocols. Their goals are approximately similar. But routers that employ them shares different kind of data to get the job done. Now lets discuss the Distance Vector protocol First:

Distance Vector Protocol

This is an older standard of routing protocol. Router that using Distance-Vector basically takes it routing table (which is a list of network) and how far away these networks are in term of hops. Then sends this list to every neighboring router.

In Computer Science list refers to as vector. This is because the protocol just sends the list of distances to networks refers to as distance vector protocol. In this protocol routers don’t really know much about the total state of an autonomous system. -The routers just have some information about their immediate neighbors. To understand Distance vector protocol let’s see how two router’s routing table might influence each other.

Routing Protocols | Routing Basic Concept | Networking Fundamentals

Consider router A has routing table with bunch of entries. One of its entry is, which refers to as Network X. Router A thinks the quickest way to Network X through Router C from its own interface. So it will take 4 hops to get to the destination. Meanwhile Router B is only 2 hops away from Network X. This information is in Router B‘s routing table. Hence Router B using Distance vector protocols sends the basic contents of its routing table to router A. Router A look that Network X is only two hops away from router B. Therefore router A then updates its routing table and forward traffic through router B instead of router C in order to reach Network X in a faster way.

So distance Vector protocols are very simple. But they don’t allow routers to have much information about the state of the world outside their own direct neighbors. Because of this a router might be slow to react to a change in a network far away from it.

Link State Protocols

So to avoid such problem in distance vector protocol, Link State Protocols eventually come into place. Routers using this protocol take a more sophisticated approach to determine the best path to a Network.

The protocols got their name ‘Link State Protocols’ because every router advertises the state of the link of each of its interfaces. These interfaces can be connected to other routers or their could be direct connection to Networks .So each router on the Autonomous System propagates this information of every other routers. This means every router on the system knows every detail about every other router in the system.

Routing Protocols | Routing Basic Concept | Networking Fundamentals

Each router then uses this much larger set of information and runs complicated algorithm against it to determine the best path to any destination network. Therefore Link_State_Protocols require more memory to hold this large data. It also needs much more processing power. Because it runs algorithms against this data to determine the quickest path to update the routing table.

As Computer hardware has become more powerful, also more cheaper over the years. Therefore link state protocols have mostly made distance vector protocols outdated.

Exterior Gateway Protocols

The exterior gateway protocols are really key to the internet operating how it does today. Since routers sharing data using ‘Interior_Gateway_Protocols’ are all under control of same organization. Hereby Routers using Exterior_Gateway_Protocols when they need to share information across different organizations.

The internet is an enormous mesh of Autonomous Systems. At height level the core internet routers need to know about autonomous systems in order to properly forward traffic.

Since Autonomous Systems are defined collection of network, therefore getting data to the edge router of an Autonomous Systems is the number one goal of core internet routers.

Internet Assigned Number Authority (IANA) a non profit organization that helps manage things like IP address allocation. Internet couldn’t function without a single authority for these sorts of issues. Otherwise anyone can use any IP space they wanted, which would cause total chaos online. Along with managing IP address allocation the IANA also responsible for ASN allocation. Here ASN stands for Autonomous System Number. ASNs assigned to individual Autonomous Systems.

Similar to IP addresses ASNs are also 32-bit Numbers. But unlike IP addresses they normally referred to as just a single decimal number instead of being split out into readable bits. Because, an ASN, never needs to change in order for it to represent more network and hosts. It just the core internet routing tables that need to be updated to know what the ASN represents. Also because ASNs are looked at by human far less often, than IP addresses are. For it represents an entire Autonomous System. For example, it is enough just being able to look at the fact that AS19604 belongs to IBM.

Non-Routable Address Space

As we have discussed in NAT that there are three range of IP addresses. These addresses are non routable anywhere by core internet routers. Which means these addresses belongs to no one and anyone can use them. In fact these addresses are totally separated from the way traffic moves across the internet. Therefore Interior gateway protocols will route these address spaces. So these addresses are appropriate to use within an Autonomous System, but exterior gateway protocols will not.

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