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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).
A group of tell-tales showing lights for "brake fluid", "stop lamp" and "check engine" Graphical tell-talesA tell-tale, sometimes called an idiot light [1] or warning light, is an indicator of malfunction or operation of a system, indicated by a binary (on/off) illuminated light, symbol or text legend.
Trafficator in the "on" position Trafficator in the "on" position Austin A30 with trafficator deployed. Trafficators are semaphore signals which, when operated, protrude from the bodywork of a motor vehicle to indicate its intention to turn in the direction indicated by the pointing signal.
Dashboard instruments displaying various car and engine conditions. Where the dashboard originally included an array of simple controls (e.g., the steering wheel) and instrumentation to show speed, fuel level and oil pressure, the modern dashboard may accommodate a broad array of gauges, and controls as well as information, climate control and entertainment systems.
A port knock setup needs a firewall that logs every port access, a daemon which has means to change the firewall rules (!), and, depending on how complex the knock sequences should be, cryptographic hash generators, handling of multiple knock attempts coming in at the same time, etc.
When an outbound connection from a private endpoint passes through a firewall, it receives a public endpoint (public IP address and port number), and the firewall translates traffic between them. Until the connection is closed, the client and server communicate through the public endpoint, and the firewall directs traffic appropriately.
Headlight flashing is the act of either briefly switching on the headlights of a car, or of momentarily switching between a headlight's high beams and low beams, in an effort to communicate with another driver or drivers. The signal is sometimes referred to in car manufacturers' manuals as an optical horn, since it draws the attention of other ...
To detect knock, a piezoelectric knock sensor (basically a microphone) bolted to the engine block responds to unique frequencies caused by engine knock. The sensor generates a small voltage that is sent to the electronic control unit , which processes the signal to determine if, in fact, knock is occurring.