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ifconfig - does it look beyond its subnet?

Posted on 2004-10-13
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Last Modified: 2013-12-16
When I plug my linux box directly into the cable modem, among other info, "ifconfig" returns the address assigned to me via DHCP by the ISP.

When Im plugged into a router and then to the cable modem, "ifconfig" returns the local subnet ip (192.168.0.5 in my case).

Is there a command other than ifconfig that can return my cable modem's ip address from a linux box thats behind a router?  I want to script my box to monitor the ip address then do something when it changes... it seems that unless Im plugged directly into the cable modem, there is no way to find out that info.. even traceroute to an outside address seems to start at the gateway.
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Question by:meuedyn
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by:chris_calabrese
chris_calabrese earned 100 total points
ID: 12302645
Your Linux box sees only its local subnet and knows that the rest of the word is on the other side of the router, hence it has no need to know what the address of the router's outside interface is.

There may be a way to ask the router what IP address it has on its outside interface, depending on the type of router. Routers meant for home use usually let you get this through a web-based admin interface. In theory, you could write a script that logs into the router via the web interface, gets the IP addressing info, and parses the HTML for the answer.
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by:blkline
ID: 12302917
I'd recommend that you look at www.dyndns.org   

They have a tool that will provide DNS services for you, changing the IP address as appropriate.  You can get this as a freebie (depending on what you want) so the price is right!
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Luxana earned 150 total points
ID: 12304120
>Is there a command other than ifconfig that can return my cable modem's ip address from a linux box thats behind a router?

easiest way is use browser on linux box and have look on webpag like this:

http://www.ipchicken.com/

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