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This is a follow up to question., please bear with me., i dont have enough privilege to comment on there.,

I am new to Networking., the Answer is really confusing., If i ping to google or facebook., it only passes nearly 18 routers (traceroute) ., but are there more routers connected in between.? how will they manage to connect any point to point in the world with just less than 255 routers ? so the Edge routers alone count ? Please elaborate.

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Downey_HUff
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This is a question which I think the professional network engineers find very basic. But when asked to explain exactly and clearly why we don't need 255 intermediate hops/routers... well, it's rather hard to explain in simple terms.

The best explanation I've ever come up with is to consider the town or city in which you live: Consider a starting point (at some address in the city) and a desired ending point (also in the city.) Next, select a path (a set of directions) to get from the start to the end. (This is NOT how the Internet works.) How many steps are there in your instructions from start to end? ...4, 5, maybe even 8. But you simply will not need 255 steps to get from one place to another. Next, repeat the exercise from your home address to some place (like a famous museum) on the other side of your country. Again, you will find a surprisingly small number of steps are actually needed.

This result comes from concepts in (if I recall correctly) graph theory from mathematics. It is simply the nature of a connected graph where you have nodes and "edges" (the connections between nodes) passing information (packets on the Internet in our case.) Because the Internet is intentionally designed and built so that you can go to a nearby node (router) which then makes a good decision about where to go next, you effectively go "up" just a few hops and soon find your packet on it's way quickly "over" and then a few hops "down" to the destination.

Wikipedia has a great introduction to Graph Theory.

Craig Constantine
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  • Also many networks often end up "compressing" the number of TTL-reducing hops to less than the number of routers you actually transit, for a variety of reasons. Really the question is "will I cross 255 devices which are IP-aware and will decrement the TTL", which is quite a lot different from how many hops will you really transit, and is much less likely. – Nick Bastin Dec 22 '15 at 03:42
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I think it is helpful to picture the Internet as not a giant mesh of networks, but more like a tree, with the large, Tier 1 providers acting as the root (or roots) of the tree. So it is only a handful of hops from anywhere to a Tier 1 provider, and then a handful of hops through the provider (or to another provider), and then back down the tree. The largest number of hops I can remember seeing is about 30 from Washington DC to Mongolia. It really is a connected world.

Ron Trunk
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