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Special Forums IP Networking Help me understand ports and port forwarding please Post 302838959 by syregnar86 on Wednesday 31st of July 2013 02:11:39 AM
Old 07-31-2013
Help me understand ports and port forwarding please

I have a few questions below on ports.

From my understanding ports are what allow information to come into your computer and each port interprets/allows specific information/data to come in. Is this correct from a ball park perspective? If not could some elaborate on this please.

What commands from terminal can I run to scan for open and closed ports on my mac?

My friend and I tried doing a remote log in to each others mac books using ssh and received a port 22 error. I've heard that you can reroute or forward this port 22. What is my computer actually telling incoming information to do when it forwards a port?

Last question, opening up these ports (port 22 for example), I would think would create a security risk. Therefore, how much at risk are the two computers with an open port 22 and how on earth can ssh be secure if it requires an open port.

I apologize for having so many questions however understanding IP addresses and using the ssh command really requires some basic knowledge on how ports work.

Last edited by syregnar86; 07-31-2013 at 11:46 AM.. Reason: spelling
 

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APLAYMIDI(1)						      General Commands Manual						      APLAYMIDI(1)

NAME
aplaymidi - play Standard MIDI Files SYNOPSIS
aplaymidi -p client:port[,...] [-d delay] midifile ... DESCRIPTION
aplaymidi is a command-line utility that plays the specified MIDI file(s) to one or more ALSA sequencer ports. OPTIONS
-h, --help Prints a list of options. -V, --version Prints the current version. -l, --list Prints a list of possible output ports. -p, --port=client:port,... Sets the sequencer port(s) to which the events in the MIDI file(s) are sent. A client can be specified by its number, its name, or a prefix of its name. A port is specified by its number; for port 0 of a client, the ":0" part of the port specification can be omitted. Multiple ports can be specified to allow playback of MIDI file(s) that contain events for multiple devices (ports), as specified by "Port Number" meta events. For compatibility with pmidi(1), the port specification is taken from the ALSA_OUTPUT_PORTS environment variable if none is given on the command line. -d, --delay=seconds Specifies how long to wait after the end of each MIDI file, to allow the last notes to die away. BUGS
aplaymidi handles "Port Number" meta events, but not "Port Name" meta events. SEE ALSO
pmidi(1) playmidi(1) AUTHOR
Clemens Ladisch <clemens@ladisch.de> 2 Nov 2011 APLAYMIDI(1)
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