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I'm reading a book about computer network theory, and one topic is discusses is routing algorithms. It only mentions (probably not intentionally) how routers participate in forming the understood network topology stored in each routers memory - the routing tables.

So this brings me to my question, do Host acts like dedicated routers in this case and participate in and become part of that understood topology of the network in nearby routers?

For example, it says that routers communicate with each other to form their routing tables to find the best path. Do hosts as end user machines find themselves in this routing table (as an entry in dedicated router, routing tables) or routing topology? Do they participate in forming it?

Likewise do Computer Hosts, have entries for nearby dedicate routers in their routing tables? I'm trying to find the relation ship between a router and a host in the this process.

The issue I'm having, is if they don't participate in this process, how do the routers not where the end user machines are in the topology?

Thanks :-)

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I believe you are talking about the Internet and the IP. Here are answers of your questions:

First note the internet is a network of networks. Networks communicate with each other through routers. These big networks are like the ISP, your university or a big organization. Your computer belong to a small network in your ISP subnetwork. This small network is probably your WiFi switch and your computer.

  1. Do hosts find themselves in the routing tables ? NO, but from the IP address of the host and its subnetwork, a router can tell whether they belong to the same subnetwork or not. If they do belong, then there is no need to route the message to another router. The message is simple sent down the subnetwork. You have to study in this case the BGP protocol and the structure of IP.

  2. Your host got nothing to do with routing. The ISP takes care of all that. or your cellular company if you are using your mobile phone .. or etc .. It would be hugely complicated to let these terminals take care of that. Again, you must have a look on the IP structure.

  3. If you try to send a message to X, then your router will look at X (which has an address probably similar to 122.23.12.11 or whatever !) from the upper digits, the router (which is your ISP router in this case) will know which neighbor router to send it to. In general, Internet routing is greedy. How a router selects its neighbors ? [that's another topic]

One advice: dont look to the Internet from a pure theoretical point-of-view.

I guess I answered your question ?

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  • $\begingroup$ :-) Thanks. Does the Internet still use routing tables to find the right path or does it just use the subnet mask, how are these related? $\endgroup$
    – rubixibuc
    Commented Nov 28, 2012 at 4:45
  • $\begingroup$ It uses both. A router needs routing tables to know its neighbor routers. It cannot know all routers in the Internet, so it route to the closest routers. It is a really big domain. Asking such questions will make surf deep in that ocean ! $\endgroup$
    – AJed
    Commented Nov 28, 2012 at 4:47
  • $\begingroup$ One more quick question, is the subnet mask stored in the routing table entries as well, how else would it know where the hosts are $\endgroup$
    – rubixibuc
    Commented Nov 28, 2012 at 4:52
  • $\begingroup$ have a look at this: en.wikipedia.org/wiki/IP_forwarding_algorithm $\endgroup$
    – AJed
    Commented Nov 28, 2012 at 5:10

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