DNS Basics | Footprinting Methods and Tools

Let take at least a couple of minutes to go over some basics—mainly because you’ll see this stuff on the CEH exam. The simplest explanation of DNS I can think of follows. DNS is made up of servers all over the world. Each server holds and manages the records for its own little corner of the globe, known in the DNS world as a namespace. Each of these records gives directions to or for a specific type of resource. Some records provide IP addresses for individual systems within your network, whereas others provide addresses for your e-mail servers. Some provide pointers to other DNS servers, which are designed to help people find what they’re looking for. 

Port numbers are always important in discussing anything network-wise. When it comes to DNS, 53 is your number. Name lookups generally use UDP, whereas zone transfers use TCP.  

Big, huge servers might handle a namespace as big as the top-level domain “.com,” whereas another server further down the line holds all the records for “mheducation.com.” The beauty of this system is that each server only has to worry about the name records for its own portion of the namespace and to know how to contact the server “above” it in the chain for the top-level namespace the client is asking about. The entire system looks like an inverted tree, and you can see how a request for a particular resource can easily be routed correctly to the appropriate server. For example, the server for anyname.com in the third level holds and manages all the records for that namespace, so anyone looking for a resource (such as their website) could ask that server for an address.