Well as with a lot of things in the IT world, the answer is not simple…infact "it depends" :-)
If you use IP addresses instead of hostnames you are sure that you're still doing tests even if DNS/WINS/… are failing. But then again it might be good to know when these are failing too…. And it's always easier to use names instead of IPs… In SA we also do some caching of the IPs, that way a very temp glitch of the resolver (DNS/WINS/…) won't harm. Now how much does it "cost" to do name resolution? Again "it depends". Is the name known and already within the OSes cache or not? Is the name known by the primary resolver (DNS/WINS) or does it have to do a look-up? Or are we talking about a broadcast resolving? In most cases if the resolving can be done using Wins/DNS then the "cost" will be very low….we're talking about something like 100ms (that is IF the resolver is local and not on some far-away WAN…you see again "it depends"). And in some cases using the IP will give different results then using the hostname. For example a URL check using http://ip-address (http://ip-address) is something else then http://www.somedomain.com (http://www.somedomain.com) Often the http://ip-address (http://ip-address) will lead you to some default Plesk/CPanel/DirectAdmin/…. page while http://www.somedomain.com (http://www.somedomain.com) will give you the actual website. Also for the Windows bases systems you can see that doing a net view \\ip-addresss (file:///\\ip-addresss) or net view \\net-bios-name (file:///\\net-bios-name) or net view \\dns-name (file:///\\dns-name) will not always give the same result, although we're talking about the same system in all 3 examples. So the best answer to give is "it depends" :-) Dirk Bulinckx. Network Monitoring by Servers Alive - http://www.woodstone.nu DNS Hosting with ipv4 and ipv6 on http://www.stellardns.com From: Servers Alive Discussion List [mailto:[email protected]] On Behalf Of Barry George Sent: Thursday, March 29, 2012 6:16 PM To: Servers Alive Discussion List Subject: [SA-list] IP vs. DNS lookup Dirk/Community, In your tests throughout the years with SA, how expensive is it in terms of Guest system resources (and best practices) is it to use Host DNS lookups as opposed to using IP addressing for Host identification on checks? Barry George 807 346-2546 IT Department Dougallmedia Thunder Bay Television CKPR /CJSD /CFNO /CFQK Radio TBnewswatch.com / The Source Newspaper To unsubscribe send a message with UNSUBSCRIBE in the subject line to [email protected] If you use auto-responders (like out-of-the-office messages), make sure that they are not sent to the list nor to individual members. Doing so will cause you to be automatically removed from the list. To unsubscribe send a message with UNSUBSCRIBE in the subject line to [email protected] If you use auto-responders (like out-of-the-office messages), make sure that they are not sent to the list nor to individual members. Doing so will cause you to be automatically removed from the list.
