Reverse DNS check, Google's documented method (Apple and Common Crawl use the same idea). Verified October 7, 2026 with the example IPs from the Google and Apple docs.
What it proves: the IP's reverse name belongs to the operator AND resolves back to the same IP. What it does not: it says nothing about robots.txt compliance.
Replace the example IPs with the IP from your log.

host 66.249.66.1
# 1.66.249.66.in-addr.arpa domain name pointer crawl-66-249-66-1.googlebot.com.
host crawl-66-249-66-1.googlebot.com
# crawl-66-249-66-1.googlebot.com has address 66.249.66.1   <- must match the original IP
host 17.58.101.179
# 179.101.58.17.in-addr.arpa domain name pointer 17-58-101-179.applebot.apple.com.
