Unable to find WAN interface name (1841)

Unanswered Question
Apr 27th, 2009


While still learning I am unable to find the name of the wan interface port on my Cisco 1841. According to SDM I need at least two interfaces to set up a NAT to provide Internet for my LAN hosts, I therefor assume I need to configure the WAN port and LAN port.

While the LAN port is titled FastEthernet0/0 in the configuration file, I cannot find the name of the WAN port in there. I have read the documentation available and searched around for it but unable to find any solution to my problem.

Any help is greatly appreciated.

I have this problem too.
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Giuseppe Larosa Tue, 04/28/2009 - 00:37

Hello Craig,

it may be time to start to access via telnet the router.

access via telnet or console and type

show ip interface brief

this lists all interfaces their name and current state

up/up means fine

Hope to help


cdavies74 Tue, 04/28/2009 - 01:18

Hi Giuseppe.

Ran show ip interface brief and it only listed FastEthernet0/0 and FastEthernet0/1. Maybe I'm getting it wrong but I thought the cable from the modem would go into the port labeled "CTRLR T1/E1 0" on the router to supply Internet.

Should I instead connect the FE0/1 to the modem and configure the FE0/1 port with my ISP information (IP, Submask etc.)?

Thanks again.

Giuseppe Larosa Tue, 04/28/2009 - 03:28

Hello Craig,

ADSL modems and cable modems usually provide a LAN interface to connect to, so you should connect it with a stright cable to fas0/1.

A T1/E1 interface can have an RJ45 cable but it is a totally different pinout and can connect via a balun to have two BNC cables going to the WAN provider.

It is highly probable that your WAN interface is fas0/1.

Hope to help


cdavies74 Tue, 04/28/2009 - 03:44

Thanks again Giuseppe, I'll give it a try later on to see if it works out.

Davy Ad Tue, 04/28/2009 - 01:03

Hello Craig ,

You can also try "Show controller"




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