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TOPIC: NAT newbie

NAT newbie 11 years 4 days ago #10239

Warm Regards,

Today in class, we were introduced to NAT and its concept. Later, we were supposed to configure NAT onto 6 networks using 5 pcs and 5 routers + 2 switches. Can anyone shed some light as to how do I go about the configuration and also the router setup and its syntax?

Do hope to obtain your guidance as I am still a baby in networks.

Thanks. :lol:
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Re: NAT newbie 11 years 4 days ago #10252

  • nske
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Hello & welcome ;)

The big deal about NAT, is to understand the concept in detail. The procedure NAT follows is fully automated, so you only need to define very few things on your implementations. The exact syntax differs from router to router, but if you understand the concept of NAT you'll only need a few seconds to verify it through the proper manual page.

My suggestion is that you read carefuly this, and then check a couple of rule-examples for your router. If you don't find any (i.e. at your manual or notes), just ask here and mention what type of equipment or software you use and what you want to do, so that we provide some examples :)
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Re: NAT newbie 11 years 4 days ago #10259

Thanks for the advice. I have to configure the NAT onto Cisco routers and 2950 switches. My network diagram has 6 networks with a /27 subnet and 6 vlans. Could you advice on how do I go about setting up the router configuration? What are the syntax for NAT in the cisco routers? Since, the vlans are involved does the NAT configuration affect sub-interfaces?
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Re: NAT newbie 11 years 3 days ago #10291

  • nske
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well, personally I don't have any experience with cisco but from what I gathered from a brief reference at the IOS manual here's what you'll generally have to do (as an example).

1) Go through each one of the internal router's interfaces, virtual or not, and (assuming their addresses are already properly configured) issue the following:

[code:1]interface InterfaceName
ip nat inside
[/code:1]

2) Define to the interface that belongs to the public network

[code:1]interface InterfaceName
ip nat outside
[/code:1]

3) Define a NAT pool that you are going to use

[code:1]ip nat pool pool_name 1.2.3.4 1.2.3.4 prefix 24[/code:1]
IP1 and IP2 are changed to correspondigly the minimum and maximum addresses of the public address range you want to use. IP1 and IP2 can even be the same address, which means you'll have "NAT overloading" (addresses from all the interfaces translated to the same public address).

4) Define to the NAT engine that any packet coming from an address defined on the Access List 7, should be translated to one of the addresses of pool_name.

[code:1]ip nat inside source list 7 pool pool_Name overload[/code:1]

Since in the example we only use one address for that pool (1.2.3.4), we also define that with the argument "overload" in the end.

5) Finally, we define what address ranges should be included in Access List 7. We should include all the addresses that are supposed to exist in each of networks that the router has interfaces in.

[code:1]access-list 7 permit 1.1.1.1 0.0.0.31
access-list 7 permit 1.1.2.1 0.0.0.31 [/code:1]

In this example we add two address ranges in this access list, 1.1.1.1 - 1.1.1.31 and 1.1.2.1 - 1.1.2.31.
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Re: NAT newbie 10 years 11 months ago #10369

thanks nske....

i will try that in the network lab and see what happens. will let u know if i reach the "peak of everest" with this.
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