I just recently found out that routers connect you to the internet, but then I found out that ISPs also connect you do the internet. Can someone explain to me what really happens behind the scenes? Why do we need ISPs if our routers can connect to the internet by themselves?
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> Why do we need ISPs if our routers can connect to the internet by themselves?
Your router connects your computers to each other, and to a computer owned by your ISP.
If you don’t have an ISP, the various computers and devices in your house can upload and download information to each other, but there’s no path for information to flow between your house and Reddit (or Google, or the tiny company that’s somehow still hosting this one obscure niche site from 2003).
Basically, someone has to own and maintain the backbone routers and switches. The big ISPs then pay for rights to use those backbone routers, and then sell that bandwidth to smaller ISPs who do the same. Eventually it filters down to you having to pay an ISP for rights to use the bandwidth they are renting from the next bigger company in the chain.
Why ISPs and not individuals? It’s because it takes specialized knowledge to program and protect these switches from both physical and cyberattacks. There are also things such as liability for the data being transmitted, guaranteed uptime requirements, and even just basic stuff like who owns what IP has to be handled by someone who can be trusted to handle it right and handle it consistently. There are also serious implications to national security if those backbone routers were compromised.
All of these costs and responsibilities combined are far more than the average person could ever hope to afford or do on their own. Hence, we have ISPs.
Can you elaborate on “routers connect you to the internet”? You can’t connect to public domains without a public IP address, which you would only get as a consumer from an ISP
Computer networking boils down to sending and receiving information from one computer to another.
Now think of this like a delivery problem. Imagine you need to deliver something (the information) with your car from your house (your computer) to somewhere else (another computer). To oversimplify, your driveway is the router/modem, the street you live on is a small part of your ISP. Both of them together connect you to a much more sophisticated road network which is the internet.
If you have an ISP but no router/modem, then you have a house that is isolated by itself with no road access. If you have a router/modem but no ISP, then you have a driveway that isn’t connected to any road, ie it’s useless pavement. You need both of them to access the bigger network.
It’s very similar (conceptually) to how the landline phone system works… You have a phone in your house, it’s connected to a local exchange, that’s connected to a regional exchange and that’s connected to an international exchange. Depending on where you’re calling, you’re phone will be connected along different paths.
If you switch perspective to that international exchange the system can be viewed as a bunch of trees (like a family tree) branching out from that central point.
Your router, is like a landline phone, connected to your ISP, which is a local provider, and they’re connected to another provider (usually referred to as a backbone providers). If your router wasn’t connected to your ISP, your computer’s could talk to eachother, but couldn’t talk outside your home, and if your ISP wasn’t connected to a backbone provider (as sometimes happens) you’d be able to connect to some sites (like your ISPs own website) but not all sites, depending on where exactly the break is – similar to how an international exchange problem might stop you calling the UK, but you could still call Canada or Mexico
Your router have one of the simplest routing configurations possible. It just sends all local traffic to the local interface and all other traffic to the one uplink router. That is as simple as you can make it. The router you connect to at the ISP have a much more complex configuration. Firstly it connects to a number of other home routers and need to route the traffic in multiple directions. But it is likely also connected to other similar routers to itself and will have to be able to route traffic to the next neighborhood in that direction. Most ISPs set up these routers to communicate with each other so they can configure each other. A router announces to its neighboring routers which addresses it can reach and how far away and then these neighboring routers will configure themselves based on this information and then announce this new configuration to its neighboring routers. This not only keeps manual configuration to a minimum reducing labor costs and mistakes but it also allows the routers to handle any faults. If a router loses power or a fiber connecting to routers gets damaged the routers will automatically detect this and reconfigure themselves to send traffic thorugh the remaining working connections.
On a large scale the entire Internet works the same way. In this case the ISPs use a prococoll called BGP to exchange routing information with each other. A single ISP can be connected with other ISPs though hundreds of such connections between routers. They announce which addresses they can forward traffic to and the routers find the shortest path through the Internet.
You can technically set up your own ISP with the same type of router. A lot of corporations does this. You can get what is known as a BGP peering agreement with other ISPs to carry your traffic to the entire Internet. The cost of this is actually quite low. However the ISP expects that you connect your router directly to their routers located in one of the locations they are present at. These locations called Internet Exchanges are usually not very close by, usually just one or two in each city. So you need to pay for a line going to one of these exchanges which means that it start getting more expensive then regular Internet service.
Routers route packets. They take the information you want to send and try to send it on to the right place.
This invariably means another router. Which routes them to other routers. Which routes them to other routers. And eventually, they are routed to their destination (e.g. Facebook or whatever). At the destination, their routers route them to the right datacentre, to the right server rack, to the right server, and so on.
Your home router is just the only thing in your house that “knows how” to send things to the Internet and get them back to you. It is the “default route” for your home, to talk to the wider world. All of your home router’s routes likely lead to your ISP and then the ISP routers route them out to the rest of the world. The only exception would be if you have something unusual like a 4G failover or a load-balancing multiple connection, where the “best route” for one particular packet of information might be to go one way, rather than the other (e.g. if the Facebook server is “nearer” the 4G connection or “nearer” your landline connection).
Your home router is no different to a business router which is really no different to routers in the ISPs or across the world. The only real differences are what technology they use to actually send packets (e.g. DSL, 4G, Ethernet, fibre, etc.) and how much data they are designed to handle and how much they are used to do unusual things to that data.
There’s nothing stopping you having multiple routers, or a router directly connected to the Internet in some fashion, it’s just incredibly unusual to do so and expensive. Generally, most consumers and businesses go through an ISP but some large organisations (e.g. Facebook, etc.) will have their own connection (“peering”) to other large places.
But they will have routers, just a bigger, more expensive, more powerful kind, that probably “routes” packets over fibre or other technologies. You have a home router that routes things mainly to your ISP, and probably only ever over DSL copper lines. But all your computers know what their “route” to the Internet is… the default route is listed in your computer’s network settings, and it’ll be the home router you have. The home router’s default route will be to your ISP. Your ISP will be managing dozens or even thousands of individual routes that go to destinations all over the world – satellite connection, undersea fibres, etc. And the routes for all of those will come to, say, the other end of the undersea fibre where there will be another router that knows where everything else is, and then go through another router and another as it follows the route it’s been given.
Look on your computer settings. You will find your computer’s “default route”. It’ll be your home router.
Look into the traceroute command, it’ll show you the route taken to reach any particular website from your computer. The first hop on that will be your home router, then your ISP routers then a huge number of routers all around the world, all trying to get your packet to the right place one step at a time, getting closer each time.
You are not connected “to the Internet” any differently to anyone else, the only difference is that your router only knows “The Internet is over that way”, it doesn’t know where Facebook is or how to get to it. It just knows to send it towards the ISP and that the ISP knows how to get it to Facebook. Your ISP, though, have a complicated peering arrangement which means it knows how to find all the places in the world that it needs to, and what the best route is to get to them all. Something that your router doesn’t need and probably doesn’t have (though some business routers do have those settings visible to you, e.g. BGP routing).
All your home router knows is that the ISP is saying “I can talk to anywhere, just send me the packets”, so that you don’t have to have multiple, and world-wide geographically disparate, and many different technologies to talk to all those places. You just let the ISP do it for you.
* Your ISP *is* the internet.
* It connects to other ISPs and they connect to *other* ISPs.
* The ISPs and the connections between them are what the internet is.
* Your router is a device that helps you connect many of your devices to your ISP.
* If you only have one device…you don’t even *need* a router.
the ISPs own whats called “backbone hardware”, which is the hardware that makes up critical connections on the internet.
Now then, you and your neighbour could agree to rig up your routers into an intra-net, but without a connection into these backbone routes that are owned by the ISPs, you wouldnt be able to reach any other networks.
If one of you in this neighbourhood intranet did have a connection through an ISP, you could point all of the routers in your intranet to his router as the internet gateway, and that would probably be the closest thing to “directly plugging into the internet” thats possible (although its usually against the ISPs rules).
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