CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [450]
Although you can use a Web browser, all FTP sites require you to log on. Your Web browser will assume that you want to log in as “anonymous.” If you want to log on as a specific user, you have to add your user name to the URL. (Instead of typing ftp://ftp.example.com, you would type ftp://mikem@ftp.example.com.) An anonymous logon works fine for most public FTP sites. Many techs prefer to use third-party programs such as FileZilla (Figure 25-44) for FTP access because these third-party applications can store user name and password settings. This enables you to access the FTP site more easily later. Keep in mind that FTP was developed during a more trusting time, and that whatever user name and password you send over the network is sent in clear text. Don’t use the same password for an FTP site that you use for your domain logon at the office!
Telnet and SSH
Telnet is a terminal emulation program for TCP/IP networks that uses port 23 and enables you to connect to a server or fancy router and run commands on that machine as if you were sitting in front of it. This way, you can remotely administer a server and communicate with other servers on your network. As you can imagine, this is rather risky. If you can remotely control a computer, what’s to stop others from doing the same? Of course, Telnet does not allow just anyone to log on and wreak havoc with your network. You must enter a special user name and password to run Telnet. Unfortunately, Telnet shares FTP’s bad habit of sending passwords and user names as clear text, so you should generally use it only within your own LAN.
Figure 25-43 Accessing an FTP site in Firefox
If you need a remote terminal that works securely across the Internet, you need Secure Shell (SSH). In fact, today SSH has replaced Telnet in almost all places Telnet used to be popular. To the user, SSH works just like Telnet. Behind the scenes, SSH uses port 22, and the entire connection is encrypted, preventing any eavesdroppers from reading your data. SSH has one other trick up its sleeve: it can move files or any type of TCP/IP network traffic through its secure connection. In networking parlance, this is called tunneling, and it is the core of a technology called VPN, which I will discuss in more depth later in the chapter.
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EXAM TIP The CompTIA A+ certification exams test your knowledge of a few networking tools, such as Telnet, but only enough to let you support a Network+ tech or network administrator. If you need to run Telnet (or its more secure cousin, SSH), you will get the details from a network administrator. Implementation of Telnet falls well beyond CompTIA A+.
Figure 25-44 The FileZilla program
Voice over IP
You can use Voice over IP (VoIP) to make voice calls over your computer network. Why have two sets of wires, one for voice and one for data, going to every desk? Why not just use the extra capacity on the data network for your phone calls? That’s exactly what VoIP does for you. VoIP works with every type of high-speed Internet connection, from DSL to cable to satellite.
VoIP doesn’t refer to a single protocol but rather to a collection of protocols that make phone calls over the data network possible. Venders such as Skype and Vonage offer popular VoIP solutions, and many corporations use VoIP for their internal phone networks. A key to remember when installing and troubleshooting VoIP is that low network latency is more important than high network speed. Latency is the amount of time a packet takes to get to its destination and is measured in milliseconds. The higher the latency, the more problems, such as noticeable delays during your VoIP call.
A quick way to check your current latency is to use the ever-handy PING.
1. Run PING on some known source, such as www.microsoft.com