Re: Router/Firewall Port Mapping Question
From: CheshireCat (blah_at_balh.com)
Date: 12/07/03
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Date: Sun, 7 Dec 2003 09:17:42 -0000
Hi Duane
Sockets on the PC can be client or servers.
Server/listening sockets are bound to a particular port number by an
application when they're opened. The port number is usually selected by the
people developing the application.
Client sockets are usually not bound to a port number and the operating
system will assign an available port number when the socket is opened.
With "permanent" stream connections, you have to have a Client on one side
and a Server on the other. With "temporary" datagram sockets eg UDP the
situation's more flexible and you can have a serving socket on each side
bound to a particular port number.
When a client hits the router with a request for a stream connection to an
external server, the router will open it's own client socket with a port
number from its list of available ports. This router client makes the
connection to the remote server and will forward the packets between PC
client and server until the connection is closed. I'm led to believe that in
the case of datagrams where there's no permanent connection, that if a
router receives a datagram reply within a certain time limit then it's aware
of where to forward the packet within the internal network.
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