Sybex CEH Certified Ethical Hacker Version 8 Study Guide

Understanding Network Devices 39
You must familiarize yourself with all the ports mentioned here if you are
to master the exam and become a CEH. Take the time to memorize these
ports—this knowledge will also come in handy when performing later exercises
and activities in this book.
Domain Name System
Don’t want to remember all those IP addresses? Well, you don’t have to thanks to the
Domain Name System (DNS) and its ability to translate names to IP addresses and back.
The DNS that you may already be aware of, even if you don’t actively think about it, is the
one used to translate names to IPs on the Internet. DNS is incredibly powerful and easy
to use, but at the end of the day it is simply a database that contains name-to-IP mappings
that can be queried by any DNS-aware applications.
The Internet root servers, or top-level servers, include the addresses of the DNS
servers for all of the top-level domains, such as .com and .org. Each top-level server contains
a DNS database of all the names and addresses in that domain.
Local networks that are isolated from the Internet may use their own domain name
systems. These translate only the names and addresses that are on the local network. They
often use DNS management software and protocols, which are similar or identical to those
used by the Internet implementation.
The Importance of DNS
In this book we’ll discuss many attacks against systems of which a portion will include
manipulating DNS. Although DNS is a simple service and its loss may seem only an
inconvenience, this is far from the case. In many modern environments, applications may
not work without DNS present and functioning. Tools such as Microsoft’s Active
Directory won’t work at all without DNS present or accessible.
Understanding Network Devices
We’ve covered the basic design fundamentals of common local area network layouts. Now
let’s fill in the gaps by exploring those common networking devices that you typically see in
a larger network setup.
Routers and Switches
Routers and switches are integral to the successful operation of nearly all of today’s modern
networks. For that matter, many of our home networks are now advancing to their own
local routing and switching capabilities not seen in homes just a decade ago. Remember