When viewing the result of a
ping request, I always see the
TTL value (Time To Live) of the package. As most of you know, this value is used for avoiding endless looping in the internet routing hierarchy, but I'm wondering what's the minimal value which is to be used?
Obviously, this equals twice the depth of the internet: in worst case a package must go to the backbone and back, but does anybody know what is the worldwide maximum depth of the internet routing hierarchy?
Let me explain the root of my question:
About fifteen years ago, I followed a course on IP basics (about how the internet is set up using routers), and there I've learnt about routing tables: those tables contain the information, needed to know how to connect to the next node in the routing IP network, so if a request is sent to router who doesn't know how to handle the request, he sends it to the next router, not just to the one next to him, but one with deeper understanding of the network.
As such, routers are put in layers. The first layer is the edge of the internet (connected to the internet gateways), hence those routers typically are called "edge routers". The deepest ones are in a layer, called the backbone, and those routers are called "backbone routers". It's the simple definition of a backbone router that his routing table contains the routing information of every engine, connected to the internet.
When I followed that course, the internet was set up in seven such layers, so in theory a TTL value of fifteen is enough to cover the entire internet (this is obviously not taking into the account the fact that a router is not responding or any other problem case).
Now we are fifteen years later, obviously the structure of the internet still is the same, but what about the number of layers, and is still the case that there exist routers who are aware of every engine being connected to the internet (as we now have an "internet of things", I imagine the number of items, being connected to the internet being huge, are there still machines who can handle all this information)?