What Port Should I Use?

IANA divides port numbers into three groups, well known, registered and
dynamic/private.

According to IANA, my server should not use any of the registered ports.
But if I use of of the dynamic/private ports don't I run the risk of the
port already having been assigned to some socket? Many of the
ports in the registered range are not assigned. Would one of them be a
better choice?

Dan


Dan N

On Feb 12, 9:30 pm, Dan N <d...@localhost.net> wrote:

> IANA divides port numbers into three groups, well known, registered and
> dynamic/private.

> According to IANA, my server should not use any of the registered ports.
> But if I use of of the dynamic/private ports don't I run the risk of the
> port already having been assigned to some socket? Many of the
> ports in the registered range are not assigned. Would one of them be a
> better choice?

It all depends what you're doing. You haven't given us any clues.

DS

On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:

> It all depends what you're doing. You haven't given us any clues.

Yes I have, I'm running a server, something that I need to assign a port to.

Dan

On Feb 13, 5:22 pm, Dan N <d...@localhost.net> wrote:
> On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:
> > It all depends what you're doing. You haven't given us any clues.
>
> Yes I have, I'm running a server, something that I need to assign a port to.
>
> Dan


What type of server, what port(s) are you thinking of?

On 02/14/2008 05:52 AM, Dan N wrote:
> On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:
>
>> It all depends what you're doing. You haven't given us any clues.
>
> Yes I have, I'm running a server, something that I need to assign a port to.

BTW, is it possible you elaborate a bit more what's that something and,
or server is supposed to do.

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Dan N wrote:
> On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:
>
>> It all depends what you're doing. You haven't given us any clues.
>
> Yes I have, I'm running a server, something that I need to assign a port to.
>
> Dan

Pick something not already in use.

See
/etc/services
and
http://www.iana.org/assignments/port-numbers

On Feb 13, 4:22 pm, Dan N <d...@localhost.net> wrote:
> On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:
> > It all depends what you're doing. You haven't given us any clues.
>
> Yes I have, I'm running a server, something that I need to assign a port to.
>
> Dan

That's still no information at all. What kind of server? Are you going
to be in charge of all the servers running it or will it be
distributed? What is the target user who would be installing and
managing the server? Does it use an existing protocol or a new one?

DS

David Schwartz wrote:
> On Feb 13, 4:22 pm, Dan N <d...@localhost.net> wrote:
>> On Wed, 13 Feb 2008 05:06:21 -0800, David Schwartz wrote:
>>> It all depends what you're doing. You haven't given us any clues.
>> Yes I have, I'm running a server, something that I need to assign a port to.
>>
>> Dan

something between 1-65535 should do.

On Thu, 14 Feb 2008 13:27:16 -0800, David Schwartz wrote:

> That's still no information at all. What kind of server?

It's serving widgets. Widgets servers have no IANA assigned port.

> Are you going
> to be in charge of all the servers running it or will it be
> distributed?

It will not be used enough to warrant registering a port with IANA.

> What is the target user who would be installing and
> managing the server?

Because it is serving widgets and there is no port assigned for widgets, it
will not be using well know ports. So it will not require root privilege
to run.

> Does it use an existing protocol or a new one?
If it used an existing protocol the obvious choice would be to use the
port already assigned to that protocol.

So back to my original question:
if I use one of the dynamic/private ports don't I run the risk of the
port already having been assigned to some socket? Many of the
ports in the registered range are not assigned. Would one of them be a
better choice?

Dan

On 13 Feb 2008, in the Usenet newsgroup comp.os.linux.networking, in article
<47b2807f$0$20227$(E-Mail Removed)>, Dan N wrote:

>IANA divides port numbers into three groups, well known, registered and
>dynamic/private.
>
>According to IANA, my server should not use any of the registered ports.

You can use any port you wish to. You need only live with the consequences.
The purpose of port registration is to allow others to have some clue where
to connect to your server to find what-ever service you may want to be
providing. Do you want to run it on 25/tcp or 2048/tcp - go for it, but
expect that clients are going to need to know where you've hidden it, and
what sort of protocol (not just network, like TCP or UDP or what-ever, but
the application level protocol - what words are in those packets, in what
order, and so on).

http://www.iana.org/assignments/port-numbers says that ports 0-1023 are
well known ports, providing services on most systems. I mention using
port 25 above, which is the well-known port for SMTP (mail transfer). In
the event that your system was going to send mail to another, your system
would look for a mail server on port 25 on that other server, because that
is what the protocol expects. If you wanted to run a mail server on port
27, you could do so, and not one of the Internet Police Force would come
to your house and beat you to a pulp for trying. By the same token, don't
expect to many other systems in the world to know you're on a non-standard
port. Can you say "compatibility"?

>But if I use of of the dynamic/private ports don't I run the risk of the
>port already having been assigned to some socket?

That's a problem for you when you are configuring the server. Start by
running the command 'netstat -anptu' and see what ports are in use now.
You may not want to try to use those, because any process trying to use
a port that is being used elsewhere will get an error message saying
that the port is in use, and suggesting you go elsewhere.

>Many of the ports in the registered range are not assigned.

Registered Ports are in the range 1024-49151, and please tell me if that
has stopped eleventy-zillion viruses from using those ports. Or have
you looked somewhere else and found that The Cult Of The Dead Cow has
managed to register port 31337 for the family of Back Oriface worms?

>Would one of them be a better choice?

Try it and see what happens. The worst thing you might run into is your
ISP or an upstream is tossing any packets to/from that port into the bit
bucket because it looks like yet another windoze virus, or they could
increase what they charge you because of your attempted mis-use of their
bandwidth..

Old guy