What is the most reliable, fastest way to identify the Googlebot crawler? rDNS can be spoofed, so the googlebot ip list looks to be the most reliable way. Are there any sites/resources, where the actual googlebot ips can be obtained? Any other ideas welcomed.
If you really want to have the IP hardcoded (I wouldn't recommend it, since it can change at any time and without notice), there's a list available here. What I would recommend (and, also, what is recommended on Goggle Webmaster's blog) is that you do a reverse DNS, and then a forward DNS to verify this. That should always work, and cannot be spoofed.