During the week I work as a Network/Systems Administrator. There are plenty of online tools that I use daily to make my life easier.  One of them is dnsstuff.com which lets you check everything you need about an IP-address or domainname. Iptools.com and domaintools.com are two other alternatives. For those of you who are into network administration and need to calculate those subnets and networks – check out a Subnet Calcluator.