How to get my own IP

Dar Scott dsc at swcp.com
Mon Dec 30 22:08:01 CST 2002


On Monday, December 30, 2002, at 04:55 AM, Björnke von Gierke wrote:

> I was trying to get my IP for a little chat program I wrote, but with 
> my code I always get the local IP of my subnet (192.168.1.2) To my 
> understanding it is not possible to connect to me if the other Host 
> does only know that IP. So is there a bug, is it because I coded this 
> wrong, or is that IP sufficient? (www.yanku.net is the URL of a friend 
> of mine)

Probably, none of those.  The code and IP address are fine.  You get 
the IP address of your computer.

But that is probably not what you want.

I assume you want to provide an Internet service from your computer.  
(This question has come up a few times.)

You seem to be behind a firewall (perhaps a router) and your Internet 
packets are subject to Network Address Translation (NAT).  There are 
two common methods (and combinations).  With masquerade NAT, all 
computers for this service share the IP address of the firewall as 
viewed from the outside.  With fixed NAT, your computer will have a 
fixed public address, one that is not the same as you get with your 
tests.

If your case is the latter (fixed NAT), find out what that address is 
and use that.  If your case is the first, this takes a little more work.

Typically, a firewall can have a setting so that a service on an inside 
computer can be exposed to the outside.  The firewall typically listens 
on a port for that service and then translates it to the port and 
computer specified.

There are a few web sites that will probe back and get the IP address 
your connection seems to be coming from and those might give you some 
information that will help.  (I'm on a new computer and don't have my 
bookmarks moved over, but I think if you go to grc.com, click on 
"Shields Up! and follow the directions you will get some information.)

Dar Scott



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