Ports in any system located in a common network hierarchy play the role of connecting elements. Knowing which one is open or closed, an application from one node can send a message to the same application on another. Why and how you can open the port in Linux, this article will tell.
Bit of theory
The port is expressed by a number from 0 to 65535. Many values are registered for official needs, some can be used arbitrarily. The port defines a kind of address refinement. For example, a certain resource has a web server running at home.
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- 23 - Telnet;
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- 110 - POP3 ( ).
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iptables -A INPUT -p tcp -m tcp --dport 53 -j ACCEPT
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