Determining Real IP of Cable Router

[alisajid]

I'm using a cable modem based internet service plugged into a small Linksys DSL/Cable router with built in DHCP server and ethernet switch.
Basically, I enabled port forwarding on the router to allow external users to get in to a machine on the private network. Unfortunately, the IP address handed out by the cable company is dynamic. I need to be able to determine my real IP (i.e. the router's real IP).

I was thinking of writing a small perl script (executing in a cron job) that opens up a cgi based page on a public machine on the internet that records the remote host header then have that perl script email me the address.

I was hoping that someone could tell me a better was of doing this using some sort of IP family protocol such as ICMP to determine the true address of my firewall without resorting to trickery.

 

[Tallgeese]

<< Basically, I enabled port forwarding on the router to allow external users to get in to a machine on the private network. Unfortunately, the IP address handed out by the cable company is dynamic. I need to be able to determine my real IP (i.e. the router's real IP). >>

A Dynamic DNS service (like tzo.com) loaded on the internal target machine would allow you to have a &quot;permanent&quot; address (like target.yourdomain.com) to aim for. No programming involved, but a yearly fee is involved ($35 for basic service to an address like machine.tzo.com).

 

[konichiwa]

There are many free sites like this (dyndns.org and others that I can't think of right now)

 

[formulav8]

no-ip.com is probably one of the better free ones

 

[bot2600]

Now where is a cheap place to register a domain name and we are set!

Bot