Re: [lwip-devel] TCP source port numbers

[Kieran Mansley]

On Mon, 2011-04-11 at 12:40 +0100, Kieran Mansley wrote:
> On Mon, 2011-04-11 at 13:31 +0200, Ullberg, Gustaf wrote:
> > Excerpt from http://www.iana.org/assignments/port-numbers :
> > "The Registered Ports are those from 1024 through 49151
> > DCCP Registered ports SHOULD NOT be used without IANA registration.
> > The registration procedure is defined in [RFC4340], Section 19.9.
> > The Dynamic and/or Private Ports are those from 49152 through 65535"
> 
> I believe that is for listening ports, i.e. where you're running a
> server that needs a well-defined port number so that the other end knows
> where to contact it.  For the active open end of the connection the
> source port is less restricted - try doing a connect (without a local
> bind) on any Linux system for example and see what source port you get
> given by the OS.  I'm pretty sure it will fall into the range you're
> worried about.

Looking into this in more detail the behaviour varies considerably
between operating systems.  Wikipedia seems to have a reasonable
summary:

http://en.wikipedia.org/wiki/Ephemeral_ports

It seems as though people are gradually standardising on using the IANA
unregistered range though, so perhaps we should follow suit as you
suggest.

Feel free to file a bug, and I'm sure it will get fixed, although it's
pretty low priority.

Kieran