NAT network address translation

NAT network address translation for
sharing internet connections and more

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NAT Basics
Published: 5-Feb-2001
Overview
NAT is an acronym for Network Address Translation. It is a commonly used IP translation and mapping technology. To home networkers like you, it is a technology that allows your home network to share internet access. Using a device or piece of software that implements NAT allows an entire home network to share a single internet connection over a single IP address. A single cable mode, DSL modem, or even 56k modem could connect all the computers in your home to the internet simultaneously. Additionally, NAT keeps your home network fairly secure from hackers. 
NAT is built in to the most common Internet Connection Sharing technologies around. Microsoft has built their ICS around it and every Cable/DSL Broadband Router on the market accomplishes its job with NAT.
How does it work?
NAT acts as an interpreter between two networks. In the case of a home network, it sits between the internet and your home network. The internet is considered the ‘public’ side and your home network is considered the ‘private’ side. When a computer in the private side request data from the public side (the internet), the NAT device will open a little conduit between your computer and the destination computer. When the public computer returns results from the request, it is passed back through the NAT device to the requesting computer.
 
Security: Basic NAT is not a real firewall?
Basic NAT devices are not real firewalls, but they are usually considered ‘good enough’ for most home networks. By not forwarding requests or probes that originate from the internet to your LAN, a NAT device blocks most mischief. A simple NAT device can not keep hackers from running DOS (Denial Of Service) attacks on you, but individuals rarely get attacked like that. It will keep out people looking for file shares, rogue mail servers and web servers, and most port based exploits. Most also protect against SMURF and WinNuke atatcks. With a NAT device and a good anti-virus program, you should be safe from the most common kinds of internet attacks.
Stateful packet inspection (SPI)
Some NAT routers have an advanced form of firewall built in that does 'stateful packet inspection'.  This allows the NAT devices to filter out specific kinds of data on your router like SYN flood attacks, IP Spoofing, Teardrop attacks and others.  SPI is a general term that can describe a router that filters more kinds of attacks than basic NAT by closely examining packet data structures.  Of course, each manufacturer will implement different kinds of SPI so not all SPI routers are equal.  Routers with SPI can often log attacks.
What If I want to host a server?
Most NAT devices allow you to create maps between the internet and your computer network - this is called port forwarding. Example: A request on port 80 from the Internet (looking for a web server on your IP address) would normally be turned away by a NAT device.  A special mapping can be set up to send that request from the internet to a specific computer on your network. One of your LAN computers could host a web server on the Internet, and another computer (or the same one) could host an FTP server because the two services work on different ports. Only a few special programs on the internet will not work using this port forwarding system.
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157 comments
NAT network address translation for
sharing internet connections and more
adsl by kur9 - 10/8/2001 1:46:00 PM
Re: adsl by PG - 5/9/2002 2:39:00 PM
Re: adsl by Dan - 5/10/2002 4:41:00 PM
Re: adsl by Malo - 5/24/2002 3:29:00 PM
Re: adsl by nkiwi - 4/11/2003 2:50:00 AM
adsl by kur9 - 10/8/2001 5:23:00 PM
Re: adsl by shahab - 10/13/2001 2:42:00 AM
Re: adsl by clark - 10/22/2001 2:23:00 PM
Re: adsl by Chris Kaminski - 10/26/2001 11:56:00 AM
Re: adsl by Travis - 10/26/2001 6:05:00 PM
Re: adsl by abz - 2/3/2002 12:22:00 AM
Re: adsl by Dan B - 3/9/2002 12:03:00 PM
Re: adsl by DreadDave - 3/12/2002 2:00:00 PM
Re: adsl + solaris 8 by Tshiamo Motshegwa - 3/29/2002 3:10:00 PM
Re: adsl + solaris 8 by Nathan Humphrey - 6/11/2002 8:20:00 AM
Re: adsl by pravin - 9/16/2004 12:50:00 AM
Re: adsl by joe - 2/21/2007 4:03:00 PM
Posted by joe
2/21/2007 4:03:00 PM.
Re: adsl
wft is a hup? I have heard of hubs but never hups...besides. you should used a network switch instead of a hub
Linksys Router and XP ..NAT? by Mica - 11/26/2001 2:23:00 AM
Re: Linksys Router and XP ..NAT? by blah - 2/1/2002 5:02:00 AM
Re: Linksys Router and XP ..NAT? by Hyperdrive - 3/24/2002 9:31:00 PM
Re: Linksys Router and XP ..NAT? by peersaab - 7/16/2002 11:36:00 AM
Re: Linksys Router and XP ..NAT? by adlsman - 11/19/2003 11:13:00 AM
Re: Linksys Router and XP ..NAT? by ringworld - 10/22/2005 12:04:00 AM
Re: Linksys Router and XP ..NAT? by Helay - 6/28/2005 7:29:00 AM
When do you need NAT or a Router ? by Sizwe - 3/8/2002 11:37:00 AM
Re: When do you need NAT or a Router ? by Dan B - 3/9/2002 12:13:00 PM
Re: When do you need NAT or a Router ? by Gerry - 5/13/2002 6:48:00 PM
Re: When do you need NAT or a Router ? by nats - 11/19/2003 11:17:00 AM
Help How to NAT with 2 coms and a smc router by Darren - 3/11/2002 6:07:00 AM
Re: Help How to NAT with 2 coms and a smc router by Josh - 3/12/2002 8:35:00 PM
Re: Help How to NAT with 2 coms and a smc router by shudha ravi sharma - 11/30/2002 8:52:00 AM
Re: Help How to NAT with 2 coms and a smc router by dipak biswal - 2/21/2004 3:43:00 AM
Messenger and Personal Routers by John - 4/4/2002 12:12:00 PM
NAT/Wireless/VPN! by Rich Bonneau - 4/30/2002 11:26:00 AM
Re: NAT/Wireless/VPN! by Gerry - 5/13/2002 6:57:00 PM
Re: NAT/Wireless/VPN! by des - 11/15/2003 4:57:00 PM
Re: NAT/Wireless/VPN! by Ronnie Gates - 11/25/2003 3:49:00 PM
Re: NAT/Wireless/VPN! by naval gupta - 10/25/2005 10:24:00 PM
help by GEORGE - 5/8/2002 3:49:00 PM
Software Or Hardware? by Joel - 5/29/2002 8:25:00 AM
Lynksys router and iSpQ by Shelley - 6/3/2002 11:39:00 PM
Re: Lynksys router and iSpQ by Dan - 6/4/2002 1:27:00 AM
Re: Lynksys router and iSpQ by SB - 5/8/2003 3:54:00 PM
Re: Lynksys router and iSpQ by Dan - 6/4/2002 1:22:00 PM
NAT with only one Public IP by Luke - 6/6/2002 7:52:00 PM
Re: NAT with only one Public IP by Clint - 6/21/2002 9:29:00 AM
NAT/Belkin Network by Gregg - 7/10/2002 9:18:00 AM
want true NAT, DHCP - product suggestions? by Dave Atkins - 8/7/2002 2:42:00 PM
Re: want true NAT, DHCP - product suggestions? by bill carver - 8/16/2002 1:46:00 PM
NETWORKING by Alex - 8/8/2002 10:28:00 PM
NetWorking problem by palex - 8/19/2002 2:06:00 AM
Re: NetWorking problem by Andre - 8/26/2002 1:54:00 AM
Re: NetWorking problem by seelan - 9/4/2006 5:32:00 AM
XBox, Gamespy, Lynksys by Kevin - 8/25/2002 4:40:00 PM
Re: XBox, Gamespy, Lynksys by Jack The Ripper - 3/3/2003 3:44:00 PM
Installing router by James - 8/28/2002 4:42:00 PM
Re: Installing router by yogesh kumar - 8/30/2005 5:20:00 AM
Re: Security on installed Netgear MR314 Cable Router by yeah me - 9/15/2002 2:28:00 PM
Re: Security on installed Netgear MR314 Cable Router by yeah me - 9/15/2002 2:28:00 PM
need help!! by Sal - 9/16/2002 8:41:00 AM
Shared Connection by Help Seeker - 9/23/2002 3:54:00 PM
Re: Shared Connection by Laurie - 11/29/2002 6:29:00 AM
Re: Shared Connection by andy - 11/1/2004 10:31:00 AM
routin out the prob by help me plz - 10/13/2002 10:07:00 PM
Re: routin out the prob by Kain - 10/15/2002 2:03:00 AM
SMC barricade , X-win32 NAT trouble by Kain - 10/15/2002 2:01:00 AM
SMC barricade , X-win32 NAT trouble by Kain - 10/15/2002 2:01:00 AM
SMC barricade , X-win32 NAT trouble by Kain - 10/15/2002 2:01:00 AM
Re: SMC barricade , X-win32 NAT trouble by same problem here - 4/10/2003 8:11:00 PM
Re: SMC barricade , X-win32 NAT trouble by Gilly - 5/2/2003 6:05:00 AM
VPN help! - Could someone respond to this request via e-mail by Dave Liggett - 10/28/2002 12:09:00 PM
NAT and performance (page resolution) by matt weber - 10/31/2002 7:45:00 PM
online games and routers by Keith - 2/3/2003 3:29:00 PM
Re: online games and routers by Jeminie - 2/20/2003 3:37:00 PM
Cable Problems by JP - 2/25/2003 8:43:00 AM
Re: Cable Problems by GreyOwl - 3/2/2003 9:20:00 AM
Network problem by michael chukwu - 3/4/2003 10:26:00 AM
NAT by Marenello - 3/21/2003 10:15:00 PM
Re: NAT by Lee - 3/27/2003 9:19:00 AM
can't get ICS port forwarding to work by Mike - 3/31/2003 10:47:00 PM
Two PCs can not see each other by Frank - 4/2/2003 10:48:00 PM
Re: Two PCs can not see each other by SB - 5/8/2003 4:03:00 PM
NAT by Nami - 4/7/2003 3:37:00 PM
Sharing ASDL over Network by Paul - 4/9/2003 5:14:00 PM
Broadband + Networking by Scott - 4/14/2003 3:23:00 PM
ftp support on NAT routers by Gary - 4/16/2003 1:47:00 PM
Re: ftp support on NAT routers by vinny - 6/4/2003 12:25:00 AM
Re: ftp support on NAT routers by BlackBird - 6/12/2003 2:24:00 AM
Configure router? by brafit - 5/15/2003 10:40:00 PM
Configure router? by Jose - 5/26/2003 12:37:00 AM
Re: Configure router? by Chuck - 8/16/2003 12:38:00 PM
Re: Configure router? by mike - 11/23/2003 1:36:00 PM
5 Static IP's and a router in same workgroup by ac - 6/12/2003 2:04:00 PM
DSL-] Router -] WAP -]xp (NAT prob) by mojotaco - 6/26/2003 12:13:00 PM
Home LAN help by Ken - 7/27/2003 6:50:00 AM
HELP WITH NAT!!!!!!!!!!!!!!!!!!!!PLS!!!!! by Rascallyman - 8/15/2003 5:48:00 AM
HELP to put a wireless system by Xavier Serrano - 9/28/2003 11:42:00 PM
Re: HELP to put a wireless system by Z - 10/5/2003 6:51:00 AM
Re: HELP to put a wireless system by thedreamingfool - 11/19/2003 11:08:00 PM
Re: HELP to put a wireless system by thedreamingfool - 11/19/2003 11:11:00 PM
Re: HELP to put a wireless system by thedreamingfool - 11/19/2003 11:12:00 PM
Re: HELP to put a wireless system by Dc- - 12/11/2005 9:35:00 AM
NAT configuration in windows 2000 domain by prashanth - 11/6/2003 10:10:00 PM
using a switch and a router by Zac Noam - 2/1/2004 4:28:00 AM
Re: using a switch and a router by anonymous - 3/9/2004 10:26:00 AM
Network Drive Security by Scott Pearson - 4/2/2004 11:35:00 PM
Re: Network Drive Security by Dennis Schwab - 4/7/2004 10:08:00 PM
Re: Network Drive Security by Stu - 5/11/2004 4:00:00 AM
Is NAT blocking my access to some Web Sites by Dennis Schwab - 4/7/2004 2:43:00 PM
Document of NAT (detail), help me by dungkhdt - 4/19/2004 3:59:00 AM
Re: Document of NAT (detail), help me by Stu - 5/11/2004 4:12:00 AM
Re: Document of NAT (detail), help me by Stu - 5/11/2004 4:13:00 AM
nat not letting me play xbox game by bob - 8/16/2004 9:34:00 PM
I NEED HELP!!!!! by Coolrider - 8/29/2004 8:12:00 PM
Re: I NEED HELP!!!!! by ody - 9/1/2004 10:56:00 PM
Re: I NEED HELP!!!!! by Coolrider - 9/6/2004 9:24:00 PM
Re: I NEED HELP!!!!! by Tom - 12/26/2005 10:54:00 PM
Re: I NEED HELP!!!!! by steve - 9/2/2004 6:57:00 AM
belkin f5d7230au4 nat problems by stuart - 9/4/2004 2:19:00 AM
Re: belkin f5d7230au4 nat problems by stuart - 9/4/2004 8:38:00 PM
Re: belkin f5d7230au4 nat problems by RLC - 10/11/2005 1:57:00 AM
Network prob PLEASE HELP!!!!!!! by Coolrider - 9/11/2004 5:28:00 AM
Connecting my wireless webcamera by ani77 - 9/13/2004 11:43:00 PM
IT by martin fenton - 10/19/2004 6:23:00 AM
Internet Tecnology by martin fenton - 10/19/2004 6:30:00 AM
Re: Internet Tecnology by Vindicator - 3/14/2005 8:51:00 AM
question by gilbsme - 11/13/2004 7:32:00 AM
Re: question by Some techie - 11/30/2004 11:29:00 AM
Zoom adsl router trouble by Steve - 12/23/2004 8:53:00 AM
Re: Zoom adsl router trouble by ion25 - 3/8/2005 10:44:00 PM
network problem by greg - 4/11/2005 9:22:00 PM
NAT configuration by lina - 6/28/2005 7:35:00 AM
Re: NAT configuration by Bhawani - 5/22/2006 3:17:00 AM
nat by pram - 7/15/2005 3:11:00 AM
i want to know about NAT for routers by yogesh kumar - 8/30/2005 5:30:00 AM
Re: i want to know about NAT for routers by patrick295767 - 9/7/2005 10:56:00 AM
Share Internet by investor - 9/12/2005 9:14:00 AM
Re: i want to know about NAT for routers by oJay - 10/7/2005 10:59:00 PM
Re: i want to know about NAT for routers by ravi - 2/28/2006 6:20:00 AM
Difference B/w DOS & DoS by Lakshmikanth - 11/23/2005 8:30:00 PM
Re: Difference B/w DOS & DoS by Jith - 5/23/2006 7:36:00 AM
help by Charger - 2/7/2006 5:18:00 PM
Re: help by ravi - 2/28/2006 6:19:00 AM
NAT ROUTER by rodrigue Ibrahim - 4/20/2006 11:36:00 AM
HughesNet and VPN by triplers - 5/4/2006 10:18:00 AM
Re: HughesNet and VPN by Gerry ONeil - 6/5/2006 12:01:00 PM
network help by Davey - 7/15/2006 5:57:00 PM
Re: network help by s - 9/4/2006 5:38:00 AM
configuration NAT with cisco routers by suday - 10/5/2006 12:53:00 PM
Posted by suday
10/5/2006 12:53:00 PM.
configuration NAT with cisco routers
please i will appreciate it if u can help by sending the diagram of the connection between router and remote gateway as it is nconnected to the internet.plus the configuration of NAT.thanks
Nat by yusuf - 3/18/2007 11:28:00 AM
Posted by yusuf
3/18/2007 11:28:00 AM.
Nat
i got very interesting how network address translation is explained, more pictures can increase the level of understanding

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