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BGP or the Border Gateway Protocol is the Modern-day Postman Pat, why? Its his job to decide which route to take while delivering your mail (data packet) in this regard.
When someone drops a letter into a mailbox, the Postal service processes that piece of mail and chooses a fast, efficient route to deliver that letter to its recipient. Similarly, when someone submits data via the Internet, BGP or (Postman Pat) is responsible for looking at all of the available path, that data could travel along with picking the best route, which usually means hopping between autonomous systems.
In a very layman’s concept, while you are playing games or surfing the internet across the world, little did u know that the way you are communicating with the server and exchanging data could take so much long if this protocol didn’t exist, its that system which activates when you are residing in India, and you load up a website with it’s origin server in the United Kingdom, BGP acts as a clutch, what could have taken more than 2-3 minutes or longer happens in seconds and with such efficiency that your teeth’s remain intact, no puns intended.
Now you are using Internet from a provider named “ABC Broadband Service” it’s available in your country and the region you reside in, its not likely to be present everywhere, not even AS6453 – TATA Communications, one of the largest networks in the world, is not present everywhere, It has to rely on this system (BGP) to communicate with others, your ISP uses the BGP Protocol to communicate with ISP’S hosting the website. Thousands of miles across the continent!.
You see, the Internet is a big space, considered a network of networks, for the ease of communication it is broken up into hundreds of thousands of smaller networks known as autonomous systems (AS), each of these networks is essentially a large pool of routers run by a single organization
If we continue to think of BGP as the Postal Service of the Internet, (AS)es are like individual post office branches. A town may have hundreds of mailboxes, but the mail in those boxes must go through the local postal branch before being routed to another destination. The internal routers within an AS are like mailboxes. They forward their outbound transmissions to the AS, which then uses BGP routing to get these transmissions to their destinations.
Taking the Reference from Cloudflare – An excellent diagrammatic representation is portrayed, in regards how the BGP works in an example of just a mere 6 numbers of AS system on the Internet
Here there are only six ASes on the Internet. If AS1 needs to route a packet to AS3, it has two different options:
Hopping to AS2 and then to AS3:
AS2 → AS3
Or hopping to AS6, then to AS5, AS4, and finally to AS3:
AS6 → AS5 → AS4 → AS3
In this simplified model, the decision is pretty straightforward, AS2 Route require fewer hops than the AS6 Route, therefore is the fastest and the efficient out there, now Imagine that there are hundreds of thousands of AS systems out there and the hop count is only just a part of the routing algorithm, that’s pretty much all it is of BGP routing.
Due to this factor and that the internet is constantly changing, every day there is one new internet service provider with (Free stuff, OTT and what not) it’s the job for the Internet service providers to keep there AS system updated with the information of new routes, obsolete routes, inefficient route – which is actually done through peering sessions where Each Individual AS from ISP’s with Neighboring ISP (AS) with a TCP connection for the purpose of sharing routing information, Using this information each ISP or AS is equipped to properly route outbound data transmission coming from within (Upstream / Downstream) – To know about this particular topic, follow my detailed article.
In the end the BGP , the Autonomous system is operated by the individual ISP organization which Provide Internet to several organizations, including Domestic consumers, Schools, Offices, Government sectors, It is there duty to regularly update the routing tables so that the Internet remains fast, efficient and responsive.