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CompTIA A+ Certification All-in-One Exam Guide

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the objectives but I’ve added for completeness):

• World Wide Web (HTTP and HTTPS)

• E-mail (POP3, IMAP, and SMTP)

• Telnet

• SSH

• FTP/SFTP

• Remote Desktop Protocol (RDP)

• VoIP (SIP)

In addition to the application protocols we see and use daily, there are

hundreds, maybe thousands, of application protocols that run behind the

scenes, taking care of important jobs to ensure that the application protocols

we do see run well. You’ve encountered a number of these hidden application

protocols back in Chapter 19. Take DNS. Without DNS, you couldn’t type

www.google.com in your Web browser and end up at the right address.

DHCP is another great example. You don’t see DHCP do its job, but without

it, any computers relying on DHCP won’t receive IP addresses.

Here’s another one: Many people don’t like to send credit card

information, home phone numbers, or other personal information over the

Web for fear this information might be intercepted by hackers. Fortunately,

there are methods for encrypting this information, the most common being

Hypertext Transfer Protocol Secure (HTTPS). Although HTTPS looks a lot

like HTTP from the point of view of a Web browser, HTTPS uses port 443.

It’s easy to tell if a Web site is using HTTPS because the Web address starts

with https, as shown in Figure 21-25, instead of just http. But you don’t deal

with HTTPS directly; it just works in your browser automatically.

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