Finding Your External IP address (with PowerShell)

For many of us, the IP address of our PC is not a publicly routable one.  If I run IPConfig on my workstation, I get something that looks like this:

Ethernet adapter Lan1BuiltIn:

   Connection-specific DNS Suffix  . : foobar.net
   Link-local IPv6 Address . . . . . : fe80::3955:f42b:2d1e:1423%10
   IPv4 Address. . . . . . . . . . . : 10.234.12.123
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 10.234.12.100

But if you were to try to ping me, you’d never get to my system, since I’m behind a firewall. My IP address on the Internet, the publicly routable IP address, is quite different.

There are a lot of ways you can find out what your IP address is – there are a bunch of sites you can use:

• http://www.thinkbroadband.com/ip.html
• http://home.ipaddress.com
• http://ip-address.domaintools.com
• http://www.check-ip.net
• http://ipchicken.com
• http://checkip.org

No doubt there are a bunch more!

Recently, I’ve seen two other sites used, via PowerShell, to get your IP address. The first is http://checkip.dyndns.org. The nice thing about this site is that it returns very little data, so you can do some ‘screen scraping’ to extract your external IP address. With this site, as shown on Per Ostergaard’s blog, you could do this as follows:

$wc=New-Object net.webclient
$wc.downloadstring("http://checkip.dyndns.com") -replace "[^\d\.]"

This is pretty cool – and in discovering this, I discovered the –replace operator that I did not know about before.

The second is also interesting. The source is here.  The script looks like this:

 

## Function to retrieve external IP address.
## the external address is retrieved from the
## title header of the webpage "www.myip.dk"

function Get-ExternalIP {
    $source = "http://www.myip.dk"
    $client = new-object System.Net.WebClient
    $webpage = $client.downloadString($source)
    $lines = $webpage.split("`n")
    foreach ($line in $lines) {
        if ($line.contains("</title>")) {
            $ip = $line.replace("    <title>Your IP address is: ", "").replace("</title>","")
        }
    }
    $obj = New-Object Object
    $obj | Add-Member Noteproperty externalIP -value $ip
    $obj
}

What this script does is to first call www.myip.dk and return the page. This site is different form the earlier ones in that it puts the IP address into the title bar. The script then parses the returned page, gets the title directive, and pulls the IP address out.

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