Hi I have a question!
For IGP, all protocols have one thing in common as they find shortest path to reach the destination.
But why in internet, it is more important to path manipulation than shortest path?
Hello Zahid
This is indeed a difference between IGPs and EGPs. IGPs will find the shortest distance based on metric. Depending on the routing protocol you’re using, the metric may be hops, or cost, calculated using various parameters.
BGP which is an external gateway protocol (EGP) uses various attributes to determine the best path. This is because BGP is designed to route traffic from AS to AS. On the Internet as a whole, this is more efficient. The Internet is composed of a multitude of Autonomous Systems. The following image makes this clearer:
On a network the scale of the Internet, it is inefficient to determine the best route based on the next hop, but it is more efficent to route based on a path of Autonomous Systems. So in the above diagram, BGP will route from AS1 to AS5 using a path of 1 2 4 3 5 or 1 3 5, depending upon the attributes configured. The best path is not always the shortest.
This introduces a hierarchy of routing if you will, making large scale internet-wide routing decisions much more efficient.
You can find more info on BGP that explains this logic in the following lesson:
I hope this has been helpful!
Laz