Dynamic port use

Peter Saint-Andre stpeter at stpeter.im
Thu May 15 00:09:01 EDT 2008

On 05/14/2008 10:01 PM, John Bailey wrote:
> Ethan Blanton wrote:
>> Mayank Jain Nawal spake unto us the following wisdom:
> <snip unneeded text>
>>> I mean why user need to specify which port his application is using? What is 
>>> the need to specify the Connection port number. 
>> That is the way network services work.  A client connects to a server
>> on a particular port.  This is not something we can change.  I
>> recommend again that you find a good textbook on TCP/IP networking.
>> Ethan
> I would also note that the user doesn't *have* to specify anything when using
> the major public services since we provide the correct port numbers by default
> on all our protocols.
> The ability to change the port is necessary on at least SILC, IRC, and XMPP, as
> anyone can run these services privately and choose to use non-standard ports.
> In these cases, the user *must* be aware that the service is running on a
> non-standard port and the user *must* change the port setting on that account in
> order to be able to connect to the service.

For XMPP, it's true that you can run your own service at a port other
than 5222 (the IANA-registered port for client-to-server connections in
XMPP), but if you do that then you should advertise the port via DNS SRV
records instead of forcing the end user to manually learn about the port
number and manually configure it in the client. Here is an example (of
example.com running an XMPP service at port 3333 on a machine called

_xmpp-client._tcp.example.com. IN SRV 5 0 3333 xmpp.example.com

Your client would then resolve xmpp.example.com to an IP address and
connect to port 3333 at that IP.

But I don't know if Pidgin supports DNS SRV lookups...

My $0.02.


Peter Saint-Andre

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