Watchguard Firebox X15, Руководство пользователя

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Introduction to Network Security
6 WatchGuard Firebox X Edge
Domain Name Service (DNS)
If you do not know the address of a person, you can frequently find
it in the telephone directory. On the Internet, the equivalent to a
telephone directory is the DNS (Domain Name Service). Each Web
site has a domain name (such as “mysite.com”) that is equal to an IP
address. When you type a domain name to show a Web site, your
computer gets the IP address from a DNS server.
A URL (Uniform Resource Locator) includes a domain name and a
protocol. An example of a URL is:
http://www.watchguard.com/
Services
A service opens access from your network to a computer that is
external to your network. You use services to send e-mail or move
files from one computer to a different computer through the net-
work. These services use protocols. Frequently used Internet services
are:
• World Wide Web access uses Hypertext Transfer Protocol (HTTP)
• E-mail uses Simple Mail Transfer Protocol (SMTP)
• File transfer uses File Transfer Protocol (FTP)
• Changing a domain name to an Internet address uses Domain
Name Service (DNS)
• Remote terminal access uses Telnet or SSH (Secure Shell)
Some services are necessary, but each service you add to your secu-
rity policy can also add a security risk. To send and receive data, you
must “open a door” in your computer, which puts your network at
risk. Attackers can use open access of a service to try to get into a
network. We recommend that you only add services that are neces-
sary for your business.
Ports
Usually, a port is a connection point where you use a socket and a
plug to connect two devices. Computers also have ports that are not
physical locations. These ports are where programs transmit data.