So, I whipped up a quick python script to get the job done. Script assumes you have a file with list of IP's, one per line.
Please use the script at your own risk!
input = open('ips.txt','r') for i in input.readlines(): try: result = socket.gethostbyaddr(i) print i.strip('\n'),result except: continue
I got the following trick from my good friend Kevin to accomplish similar result using nmap:
nmap -sL -iL fileofips.txt | grep '('