[Gllug] sorts of ports

[Paul Brazier]

> A process can say to the OS "I would like to listen on port <such and
> such>, please send me any traffic that arrives for it" - commonly
> referred to as 'binding to' a port; so 'what ports are open' is based
> on the OS's idea of which ports processes have asked to listen on - so
> in some sense, that is a result ofwhat apps are running (but note
> that process-IDs, as displayed by 'ps' and 'top', are nothing to do
> with port numbers).
> 
> The only complication is that a process needs rootly powers to bind to
> a port from 1-1024 [1].

I've always been a little puzzled by ports as well.
It seems like an unnecessary abstraction layer between the IP packets
and the "service" required.
I suppose there must be historical reasons for it (perhaps there are
logical ones also?) but why couldn't the IP packet header just request
http/ssh/ftp or whatever directly (e.g. by including the string "http")
instead of going via an arbitrary "port" number? Is it just to save
space in the IP headers?


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