Pretty much everyone in the developed world today has at least passing knowledge of how to use the Internet. From a consumer perspective, using the Internet might be as simple as logging your iPad into a wireless network in a coffee shop, then opening a Web browser. IT pros know there's a lot more to it: access points, wireless controllers, a couple of DNS servers, a good firewall, and the all-important upstream Internet connection supplied by an ISP.
However, even for many people in the business, that online connection is the outer limit of our knowledge of how the Internet lives and breathes. Although it's true that unless you actually work for an ISP you probably don't have to know how the Internet sausage is really made, there are tons of ways in which it can be extremely helpful to have a general understanding.
In an age where more and more of an enterprises resources depend on external connectivity -- say, to reach a cloud service -- it's crucial to know how traffic actually gets where it's going on the Internet. Most people know that the Internet is really just an interconnected set of smaller networks, but exactly how are they connected? For example, how did the computer you're using right now know how to get to InfoWorld's website? Knowing that requires a passing understanding of DNS and the BGP routing protocol.
At the beginning of Internet access is DNS