"Google recommends using reverse DNS to verify..."
This is almost right. They recommend two steps:
1. Use reverse DNS to find the hostname the IP address claims to have. (The IP address block owner can put any hostname in here, even if they don't own/control the domain.)
2. Assuming the claimed hostname is on one of Google's domains, do a forward DNS lookup to verify that the original IP address is returned.
Comments
"Google recommends using reverse DNS to verify..."
This is almost right. They recommend two steps:
1. Use reverse DNS to find the hostname the IP address claims to have. (The IP address block owner can put any hostname in here, even if they don't own/control the domain.)
2. Assuming the claimed hostname is on one of Google's domains, do a forward DNS lookup to verify that the original IP address is returned.
The second step is the important one.