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Does my wireless router have an ip address that's independent of my computer's ip address? Is there any way to determine what that ip address is? Note: I'm not talking about the internal router ip address: 192.168.0.1, but one that is visible from the outside.

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3 Answers

up vote 3 down vote accepted

Of course. You have an external IP address on the other side of your NAT + Router device. The simplest way is to actually look at your router's configuration or status page, which will display it. Another trick is to ask someone else on the internet what your IP address is - there are numerous websites which will show you what IP is accessing them. Note that this may not be the IP address on the external interface of your router, if your ISP is performing carrier level NAT or uses transparent proxy servers.

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When I use arp -a, I get (192.168.0.1) at 0:1d:f0:61:4f:1 on en1 ifscope [ethernet]. How do I find the external IP address? –  John Berryman Dec 17 '10 at 2:39
    
Ahh... so when I go to whatsmyipaddress.com and I see a number, that's not the ip address of my computer but of my router? And when my router gets a TCP packet, it knows who to route it to internally? –  John Berryman Dec 17 '10 at 2:49
1  
@John Berryman: You're getting the idea. Your router will have two network interfaces - 1 to connect to the outside world and one for your internal network; each will have its own address. Your PC will then have an IP that is for the inside network. –  GreenMatt Dec 17 '10 at 2:55
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As @theatrus said, there are web sites that will show you the IP they see for you. One example is http://www.pingtest.net. When you go to their page, they show the IP they see for you to the left of their globe showing servers you can run a test with. At a site like this, you also can test your connection. (This is not an endorsement of their service; it's just one place you can go to see your IP number.)

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I'd assume you are talking about a network like this, and you want to know the ip represened by 1.2.3.4 in the below graph:

     eth0          eth1                    eth0
     1.2.3.4       192.168.0.1             192.168.0.2
---------( Router )------------( Hub )-----[Computer 1]
                                  |         
                                  +--------[Computer 2]
                                           eth0
                                           192.168.0.3

The simplest method is to log onto the router and see the interface address (which I assume you should have the credential to do so. This is by far the best method.

The method suggested above by others (to use a website to see your own ip address) had the advantage of being easy to use and simple, but this suffers when this network configuration occurs (NAT by ISP), where no public IP address was allocated to you:


     eth0          eth1         eth0            eth1
     2.3.4.5       10.0.0.1     10.0.0.2        192.168.0.1
---------( Router2 )--------------------( Router1 )--------.... 
         Your ISP router                Your router

This way, you will see your ISP router's external IP (2.3.4.5) as opposed to your router's external interface address (10.0.0.2).

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1  
+1 for pretty diagrams. –  John Berryman Dec 17 '10 at 3:07
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