Following on Google's lead, MSN Search has now given us the same reverse IP set-up to verify that a request from the user agent "MSNbot" is really coming from MSN.
2... Starting with the IP address (i.e. 220.127.116.11), you can use reverse DNS lookup to find out the registered name of the machine.
3. Once you have the host name (in this case, livebot-207-46-98-149.search.live.com), you can check that it really is coming from Live Search. The name of all live search crawlers will end with "search.live.com". If the name doesn't end with "search.live.com", you know it's not really our crawler.
4. Finally, you need to verify that the name is accurate. In order to do this, you can use Forward DNS to see the IP address associated with the host name. This should match the IP address you used in Step 2 -- if it doesn't, it means the name was fake.