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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... ?

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migrated from Apr 15 '10 at 10:44

This question came from our site for professional and enthusiast programmers.

Actually, maybe you are right but i really confused where to post this Personally, I think knowing how routers communicate on packets is an important part of programming, and there is no need to ask this on SF; SO is a perfectly reasonable venue.In many applications this kind of knowledge will be useful. – Berkay Apr 15 '10 at 8:28
up vote 3 down vote accepted

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

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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.

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As you said,general point of view. So you didn't answer how routers communicate? – Berkay Apr 15 '10 at 8:09
Just updated the answer with a little more info on routing. – Slavo Apr 15 '10 at 8:32

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