After renaming the machine name still able to ping the old machine name?

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http://serverfault.com – We have renamed our machine [Windows 2008 R2] name and it asked for restart. we did it. But still we are able to ping the old machine name and it responds. Strange thing is even we are able to ping the new machine name and it also responds. [I checked that whether it is different machine or not by verifying the IP address. But IP address is same. So it should be the same machine] How it occurs? How to make it recognize only new machine name? If some scripts are run, our application should work even after machine rename. But we are unable to test this as we are unsure whether machine rena (HowTos)