Router IP

I guess you may be trying to find the external IP address of the router.

If this is the case it is unlikely to be found in the registry.

Agreed. However, you may have an option. If you can find blog posting or other Internet accesses AND if the router was also NATting your connection, you may be able to find the address of the router this way.

I had a case where a user at a call center was making posts impugning his employer. We identified his BLOG login ID from his workstation, searched for the ID on the Internet, found the blog postings in which the IP was displayed (some sites use GeoIP to substitute a location but others simply post the IP), and, bravo!, we had the external IP address of his router/NAT host.