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how this works?

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#1 5ath335h


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Posted 14 August 2014 - 05:47 AM

Can someone please explain me how this diagram works?

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#2 Wand3r3r


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Posted 14 August 2014 - 10:39 AM

First issue is terms.  There seems to be a new generation coming into IT that don't seem to understand what the terms router or modem mean and end up using the word modem when they mean router.  Very simply a modem does not do NAT [network address translation] whereas a router does.


This is a key understanding to your question.


When you put in google's ip address in a browser it does not go directly to the google server.  It goes to your router which says this isn't a local address so I will forward it to the next router.  Now that packet is on the internet which is a series of routers.  The same dialog takes place until one says "oh I know that server, give the packet to me and I will send it to the server"


The same is done in reverse to get back to you from the google server.


Google network address translation for more info.

#3 Kilroy


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Posted 14 August 2014 - 11:03 AM

As Wand3r3r said, that picture over simplifies what is going on.


The client has a 10.x.x.x address which is on a private network making it non-routable.  The item listed as a modem is actually a router and it has two IP addresses, one on the LAN side which would be a 10.100.1.x address and the public 181.76.x.x address that is connected to the Internet.


Sending something to a server is rarely done via an IP address, normally it is sent to a name, like www.yahoo.com, ftp.adobe.com, or \\sever\share.  The name is resolved to an IP address via Doman Name System (DNS) or Windows Internet Name Service (WINS).  What port you send it to makes a difference and the server has to be listening on that port.  The same goes for sending the information back, if the router is not expecting it, it will be dropped, unless the machine is in the DMZ or a port has been opened using UPnP or manually forwarded.

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