Precise time to stay in milliseconds was a really early idea that wasn’t sensible, everybody resorted to decrementing by one as this was the minimal “time” utilized by a hop. As @Commander has identified, that is as we speak’s utilization.
what is the minimal worth which is for use?
A minimal default worth for TTL is often offered by the native stack (a part of the working system). There’s little purpose to alter that. The absolute minimal for a packet on the wire is 1 – solely the very subsequent hop can be reached, and the packet won’t be forwarded any additional. This successfully disables any routing. The sensible minimal will depend on its undefined diameter, however often 20 or 30 hops are considerable.
does anyone know what’s the worldwide most depth of the web routing hierarchy?
There is no identified most depth of the Web. Absolutely the most ought to be the utmost IP hop rely, however somebody constructing a ridiculously lengthy routing assemble may simply reset the worth on the doorstep. In apply, you will have to essentially seek for routes longer than twenty-something hops.
if a request is distributed to router who does not know easy methods to deal with the request, he sends it to the subsequent router, not simply to the one subsequent to him, however one with deeper understanding of the community.
That’s not appropriate – a router at all times wants some path to the vacation spot or it’s going to drop the packet. What you seemingly imply is that edge routers solely want a single crude default route and extra central routers want to make use of extra distinguished, finely-grained routes.
the web was arrange in seven such layers
You are seemingly mixing up the seven OSI layers (bodily, information hyperlink, community, session, presentation, software) with a routing hierarchy. Routing is just a factor within the community layer.
there exist routers who’re conscious of each engine being related to the web
That is known as the Web’s ‘full’ routing desk – presently at near one million prefixes and aggregated 500k routes for IPv4 (for IPv6 roughly 20% of that).1 These should be dealt with by carriers, ISP routers or well-connected, multihomed company community routers.