[Gllug] sorts of ports

[Jon Masters]

On 01 Sep 2001 11:50:31 +0100, Leigh Mason wrote:
> 
> 
> i'm having trouble visualising what's happening when people talk about
> entering a machine via port x or port y, with regard to network
> communication.

A port is purely conceptual. When you connect hardware, you connect to
physical ports, when you talk about network traffic "ports" one means an
(often 16 bit) field in each data packet describing the conceptual
"port" on the local/remote machines is in use. Whenever a TCP connection
is made over IP, it is made to a given "port" on the remote machine from
a (often does't matter which and is handled for you when connect'ing)
"port" on the local machine. This also semi happens with stuff like UDP
traffic although in that case there is no concept of a connection or
"guaranteed delivery" like there is with  TCP. A good book to read (IMO)
on this subject is the big blue Linux Networking book - although I
forget who publishes it, it's in the "Slackware" series from some
publisher or other (not O'reilly)...maybe I'll dig it up :)

> when a connection is made between two computers there is only one interface
> in action (modem for example)  that the data is being carried across. the
> interface has a 16 bit data register allowing the 65535 possible port
> numbers, but it is still just one physical port - right?

Scratch most of that, ignore the fact that you're using a modem or any
other device since it is mostly irrelevent. The "ports" we are talking
about are implemented within the software networking "stacks" and have
nothing to do with hardware at all :) You can send them using RFC 1149
if you want... :P

--jcm



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