As a network or website administrator, most often we need know everything quite well about the LAN or even WAN our hosts lying in. For example: the name of each computer in local network, network card address, IP address, shared resource, open ports; look up WHOIS information such as domain name, host provider, DNS... about some website in detail. For these, IP-Tools can become a good assistant for our network/Internet management.
Without any doubt, Wireshark (formerly called Ethereal) is currently the world's most famous, foremost free and open source network packets capture & analysis tool. Its appearance puts an end to the future of all similar business software.
Today, at this moment of rapid development of Internet and increasingly serious intrusion behaviors to network, the network security naturally became a focus in IT field. Accordingly, the network scanning technology has also become the most important one in this field. With help of Kali Linux OS's built-in abundant powerful network scanning tools, each guy full of passion can become network security expert.
For guy who wants to be a master of network (WAN/LAN, no matter it's black, red or white), without help of various off-the-shelf classical network utilities for multipurpose uses, I'm afraid your level will stay in the DOS era of last century forever. I mean, in that case, even it was you invented the whole Internet, you could not do anything interesting or exciting.
Maybe you ever found that too many computer network related books are full of boring text and web terms that let a reader feel tired and sleepy, which is the biggest obstacle for many beginners who want to learn the network technology. Then try the Head First Networking instead.