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In computer networking, port knocking is a method of externally opening ports on a firewall by generating a connection attempt on a set of prespecified closed ports. Once a correct sequence of connection attempts is received, the firewall rules are dynamically modified to allow the host which sent the connection attempts to connect over specific port(s).
In telecommunications, a network interface device (NID; also known by several other names) is a device that serves as the demarcation point between the carrier's local loop and the customer's premises wiring. Outdoor telephone NIDs also provide the subscriber with access to the station wiring and serve as a convenient test point for ...
In computer networking, a port or port number is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system , a port is a logical construct that identifies a specific process or a type of network service .
The port numbers in the range from 0 to 1023 (0 to 2 10 − 1) are the well-known ports or system ports. [3] They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the ...
In a normal forward connection, a client connects to a server through the server's open port, but in the case of a reverse connection, the client opens the port that the server connects to. [2] The most common way a reverse connection is used is to bypass firewall and router security restrictions.
The new connection attempt punches a hole in the client's firewall as the endpoint now becomes open to receive a response from its peer. Depending on network conditions, one or both clients might receive a connection request. Successful exchange of an authentication nonce between both clients indicates the completion of a hole punching ...
Against some port knocking designs, DoS attacks are a major problem, but against othes, they are impratical or would require massive resources to be effective. Again, see this for descriptions of port knocking designs. DoS attacks are a weakness of certain specific designs, not a systemic flaw in the port knocking concept.
Packet injection (also known as forging packets or spoofing packets) in computer networking, is the process of interfering with an established network connection by means of constructing packets to appear as if they are part of the normal communication stream.