Setting up NAT/WAN for the first time (1841)

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Apr 17th, 2009
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Having recently bought a Cisco 1841 and learning how to set things up by the minute I'm now at the point of understanding how NAT works.

I've set up Interface FastEthernet0/0 on the router with ip, sub mask It's also acting as a DHCP server.

My wish is for the clients on the LAN to have access to Internet. Currently sitting in SDM on a PC looking at Configure/NAT/Create NAT Configuration and the "Basic NAT" seems like a good idea but it requires me to have two router interfaces configured. I assume the other interface should be the WAN one on the router? I have a static IP from our ISP along with dns, gateway and such but I can't find where to input this data in SDM.

Any advice is greatly appreciated. Please take note that I am a novice in networking so most of your information will be new (and very helpful) to me.

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Jon Marshall Fri, 04/17/2009 - 05:49
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Sorry but i haven't used SDM but from the command line you would do the following. For this example fa0/1 is your WAN Interface -

int fa0/1

ip address <-- this is IP from your ISP

ip nat outside

int fa0/0

ip nat inside

ip route <-- this default-gateway supplied by ISP

access-list 101 permit ip any

ip nat inside source list 101 interface fa0/1 overload

You will need to add the DNS server that the ISP gave you into your DHCP config on the router.


cdavies74 Fri, 04/17/2009 - 06:28
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Thanks alot for your reply Jon, I'll be doing this on Monday and see how it turns out.

Quick questions,

1. How do I find out the name of my WAN interface port? It's labeled CTRLR T1/E1 0 on the actual router (1841). I assume you can't use the FE0/1 port as a WAN port.

2. In your example, what exactly is the int fa0/0? My guess would be that it's short for interface fastethernet0/0 (which is my current LAN port)?

Since I'm new with Cisco stuff, SDM helps a bit more initially, not that I mind doing it through the command line but there's so much syntax I yet have to learn.

Thanks again.


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