People are asking major search engines to provide a way to identify their bots to know if it is authentic. This will stop spammers from re-naming their bots to “Googlebot” or “Yahoobot” to confuse webmasters and making it easier to know which ones to block.
Most webmasters ask: “Why not give us a list of IP’s to help identify the bots?”. Read Googles response below.
“Telling webmasters to use DNS to verify on a case-by-case basis seems like the best way to go. I think the recommended technique would be to do a reverse DNS lookup, verify that the name is in the googlebot.com domain, and then do a corresponding forward DNS->IP lookup using that googlebot.com name; eg:
> 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
I don’t think just doing a reverse DNS lookup is sufficient, because a spoofer could set up reverse DNS to point to crawl-a-b-c-d.googlebot.com.”
Sean wrote an interesting post today on Verifying Googlebot