[Gllug] sorts of ports

[Leigh Mason]

> From: David Damerell <damerell at chiark.greenend.org.uk>
> Reply-To: gllug at linux.co.uk
> Date: Mon, 3 Sep 2001 10:58:47 +0100 (BST)
> To: gllug at linux.co.uk
> Subject: [Gllug] sorts of ports
> 
> On Saturday, 1 Sep 2001, 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.
>> i understand that any i/o device has to have  interface circuits to
>> communicate data transfer to the cpu.
>> and that within each interface there are registers similar to the cpu and at
>> least one of those registers is a buffer register (for data) called a port.
>> (please correct me if i'm wrong).
>> 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?
> 
> Er, not quite.
> 
> Normally your Ethernet (or modem) hardware knows nothing about TCP/IP
> at all, including IP port numbers. IP packets are entirely
> encapsulated in packets for the lower-level transport, like this;
> 
> /here's the stuff your Ethernet /this here is an IP packet   \\
> |card understands, that tells   |that the Ethernet card will ||
> |it this is for this machine and|pass unchanged to the OS and||
> \not a lot else.                \contains an IP port number  //
> 
> The OS's IP stack has an idea of what ports are open and belong to
> which processes, and passes the IP packet to the appropriate process.

when you say 'what ports are open' is this the same as what apps are
running? because that's my whole 'don't understand' thing.

leigh
> 
> -- 
> David Damerell <damerell at chiark.greenend.org.uk> flcl?
> 
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