networking - How do subnetworks communicate with each other?

  • pnongrata

    I'm a networking newbie and I'm a little bit confused about the difference between the terms:

    • Zone
    • Sub-network
    • Topology

    I've seen network diagrams where a business's network was divided into three main "zones", which seemed like just sub-networks: (1) Intranet (private subnet), (2) Extranet (protected subnet) and (3) an Internet with public-facing web servers (public subnet).

    My understanding is that you only create these zones/subnetworks when you have a business need to do so (if you don't need an extranet, don't build one!). But within these zones/subnetworks, you structure the devices & nodes according to the topology that makes the most sense.

    First of all, if anything I have said so far is incorrect, please begin by correcting me! And if "zone" is different than "subnetwork", please let me know how and why!

    Assuming I am more or less understanding the gist of things, what devices are then used to connect zones/subnets with each other? For instance, how what network devices connect a laptop inside the intranet to an FTP server inside the extranet?

    I guess at the root of this question is this: I understand that topologies exist at the network/sub-network levels to provide cabling/connection layouts. But in a situation where you have multiple sub-networks connected to one larger network, what topologies/patterns/devices/best practices, etc. apply to inter-subnet communication? Thanks in advance!

  • Answers
  • Oliver Salzburg

    The term zone is used widely for a variety of concepts. Don't put too much meaning into it.

    But the process you speak of is common. You try to divide your whole network topology into subsections. Usually, this is due to security concerns (and, as you already noticed, only when required).

    When you have separate networks, you always need a router that routes packets between the networks.

    Just like you use a router to connect your home network to the internet, you would have a router to connect the intranet to the extranet (or the DMZ, or the internet, ...).

  • Related Question

    networking - How do the routers communicate with each other?
  • Berkay

    Let's say that i want make a request a to a web page which is hosted in Europe (i live in USA).My packets only consist the IP address of the web page, first the domain name to ip address transformation is done, then my packets start their journey through to europe.

    i assume that MAC addresses never used in this situation? are they?

    First, my packets deal with many routers on way how these routers communicate with each other?, are router addresses added to my packet headers ?

    Second, is there a specific path router to router comminication or which conditions affect this route?

    Third to cross the Atlantic Ocean, are cables used or... ?

  • Related Answers
  • Donal Fellows

    IP packet routing is fairly complex, and the key to understanding it is to know that virtually every router does not know exactly where the packet is going. It just knows that that router over there knows better than it does so send the packet over to them. You could use the analogy of following a concentration gradient for a pheromone.

    Your specific questions:

    (0. MAC addresses are network local and depend on everything being Ethernet anyway. The high-capacity links most certainly aren't Ethernet, but instead use different protocols over optical fiber.)

    1. No. There's no room.
    2. Routers tell each other routes to subnetworks; only the local routers need to be able to send to specific machines (and that's what MAC addresses and ARP are for). Routers talk to each other about routes via BGP; from time to some, some ISP messes up there and large chunks of the internet cease to work. The only reason nobody does so maliciously is because there's that much traffic, most of it dull or inane, that nobody wants to receive all of it; even paranoid dictatorships have better things to do with their time.
    3. Yes, it's fiber optic cables. Normal radio would be too noisy, satellite too slow (it's a long way to geosynchronous orbit) and copper cables work but don't have the capacity.
  • Hasaan Chop

    Pick up a copy of "TCP/IP Illustrated Volume 1" and dig in.

  • Slavo

    Short answer

    First: That's why they are called routers - they route. They take the responsibility of passing along your packets, your packet doesn't know the route, only the destination

    EDIT: There are different routing schemes. What a router does is takes an incoming packet and passes it along to some other device (other router, switch, computer) based on the routing scheme. You can read an intro to some routing schemes here. For a simple explanation, imagine that each router has a routing table with IPs and subnets. Each entry in the routing table has a key (the packet destination IP), and a value (the immediate outgoing IP or subnet). When deciding where to pass an incoming packet, it takes the IP of the packet and searches in the routing table, which gives the immediate destination. The question of when and how these routing tables are constructed is even broader.

    Second: Depends. There's usually no specific path and it's different every time.

    Third: Yes, cables on the bottom of the Atlantic are used usually.

    But seriously, you need to read about networking and TCP/IP and this answer is not scientific and fully correct.