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What is a Nat Table


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#1
Drumbum667

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Well I was watching season 3 of 24 and this programmer Andrew Page on the dhow encountered a NAT table. I googled it and i just don't understand it. I also saw Kurenai talking about double Nat. Can someone tell me wat this stuff is. Thanks.
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#2
CCMike

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OK lets keep it simple
NAT = Network Address Tranlation

All that really means in simple terms is the router holds the external address from your IPS and hands out a private IP to your internal machines.

The NAT Table (or list) is a table the switch keeps to direct request for an external IP such as www.google.com to the machine that requested the address and not broadcast it to every machine in an attempt to hit the requesting machine

Hope that helps

Edited by CCMike, 18 November 2006 - 09:40 PM.

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#3
Drumbum667

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So let me see if I understand this.
A nat table is a list the switch keeps to direct the request to my machine only and not to every machine on the network. But i dont understnad what just nat is. Please xplain more in depth.
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#4
CCMike

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NAT stands for Network Address Translation

Meaning for example
your ISP gives you and address of 64.202.17.189 the nat in the router aquires that address and hands out a address of 192.168.1.100 to a machine inside your network so it's translated the ISP addy to another addy
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#5
dsenette

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http://en.wikipedia....ess_translation

NAT is like an envelope....

when your computer sends out a packet of information...that packet is "addressed" as coming from your pc's IP address...which...in a normal network is a PRIVATE ip address....the outside world (the internet) has no use for a private IP address..because...if you've got a linksys router configured out of the box....you've got the same private ip as someone else in the world...(probably 192.168.1.X or 192.168.0.x or something to that effect) so how does the internet know which 192.168.1.x machine to send the information back to?....it doesn't

your modem from your ISP (could also be a router..depending on the setup) has a single PUBLIC IP address given to it by the ISP....this is a unique address..(no one else on the planet can have that same ip address...nifty eh? your mom was right...YOU ARE SPECIAL!! :whistling: )...the "internet" knows what to do with this kind of addres...so it can send information directly to that address...

but...how does your computer know who that info is for it? or how does the router know what address inside the network to send the traffic to?

well that's where NAT comes in...

when you send a reequest for information out of your computer....the packet is addressed with the private ip of your computer (192.168.1.2) for the example) as the source ip...and the destination (google.com) would be the destination ip....so your router grabs that peice of traffic....and puts it in an "envelope" (encapsulation)...this new envelope...contains the original packet of info (source ip = 192.168.1.2 and destination = www.google.com) but this new "envelope" has a new source ip (the external ip of your router/modem....that unique PUBLIC ip that your ISP assigned to your modem/router) but the same destination....that packet travels to google...who processes the request and sends a packet back...that packet contains the info you sent in your request for information..and the information you requested (search results)...this packet has www.google.com as the source address...and your router's PUPLIC ip as the destination....when your router get's THIS packet...it recognizes the encapsulation (it's publilc ip and the source ip)...and strips the encapsulation off of the packet (opens the envelope)...inside of that envelope it just recieved from google....is your requested info (search results) that is addressed with your private ip of your pc as the source (192.168.1.2)...so now your router knows which pc on the network to send the packet to....

this all takes milliseconds in a properly working network...and it's pretty efficient...


any of that make sense?

Edited by dsenette, 22 November 2006 - 08:35 AM.

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#6
CCMike

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Yeah ..well thats the long version of what i said
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#7
dsenette

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Yeah ..well thats the long version of what i said

extremely long...my hand went a little numb on that one
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#8
Drumbum667

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Now I fully understand it Dsennete. Thank you so much.
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