Groups > comp.lang.java.programmer > #34519

Re: Picking an unused port number

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From	Nigel Wade <nmw@ion.le.ac.uk>
Newsgroups	comp.lang.java.programmer
Subject	Re: Picking an unused port number
Date	Tue, 7 Jun 2016 09:43:31 +0100
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On 06/06/16 23:40, Knute Johnson wrote:
> On 6/6/2016 05:28, Eric Douglas wrote:
>> On Saturday, June 4, 2016 at 12:56:14 PM UTC-4, Knute Johnson wrote:
>>> 8787 is always nice.
>>
>> This was an ancient thread, but...I've always wondered about port numbers, they seem so random.  There's a bunch of
>> examples here all using different numbers.
>> http://cs.lmu.edu/~ray/notes/javanetexamples/
>>
>
> Any port works until there is a conflict.  It's what you do about it then that separates the easy from the hard.
>

The best way to avoid conflicts is to allow the system to give you an unallocated port and then register that port using 
some method such as rpcbind, or in the Java world, rmiregistry. These two methods are primarily for registering remote 
procedures/methods, but can also be used for simply registering an assigned port to provide a named service.

A client can query portmap or rmiregistry to find out what port a particular service is registered, and listening, on.
The only port numbers which then need to be well defined are those used by portmap or rmiregistry. rpcbind/portmap is 
required by NFS and NIS (formerly YP). I use rmiregistry with some of my applications where I need to operate a server 
but don't wish to define a fixed port number (to avoid possible future conflicts).

Thread

Re: Picking an unused port number nathanturner369@gmail.com - 2016-06-04 08:24 -0700
  Re: Picking an unused port number Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2016-06-04 09:56 -0700
    Re: Picking an unused port number Eric Douglas <e.d.programmer@gmail.com> - 2016-06-06 05:28 -0700
      Re: Picking an unused port number Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2016-06-06 15:40 -0700
        Re: Picking an unused port number Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-07 09:43 +0100
          Re: Picking an unused port number Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2016-06-07 07:43 -0700
            Re: Picking an unused port number Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-07 17:28 +0100
              Re: Picking an unused port number Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2016-06-07 09:40 -0700
                Re: Picking an unused port number Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-08 10:32 +0100
                Re: Picking an unused port number Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 06:45 -0700
                Re: Picking an unused port number Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-08 15:06 +0100
                Re: Picking an unused port number Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 07:36 -0700
                Re: Picking an unused port number Martin Gregorie <martin@address-in-sig.invalid> - 2016-06-08 18:03 +0000
  Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-04 20:50 -0400
    Re: Picking an unused port number Wayne <wayne@nospam.invalid> - 2016-06-06 18:44 -0400
      Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-06 20:52 -0400
        Re: Picking an unused port number Arne Vajhøj <arne@vajhoej.dk> - 2016-06-06 21:28 -0400
          Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-06 21:45 -0400
            Re: Picking an unused port number Arne Vajhøj <arne@vajhoej.dk> - 2016-06-06 23:07 -0400
              Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-07 09:50 -0400
                Re: Picking an unused port number Lew <lewbloch@gmail.com> - 2016-06-07 13:46 -0700
                Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-07 19:31 -0400
                Re: Picking an unused port number Lew <lewbloch@gmail.com> - 2016-06-07 17:26 -0700
                Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-07 21:34 -0400
                Re: Picking an unused port number Lew <lewbloch@gmail.com> - 2016-06-08 13:52 -0700
                Re: Picking an unused port number Jerry Stuckle <jstucklex@attglobal.net> - 2016-06-08 17:49 -0400
                Re: Picking an unused port number Arne Vajhøj <arne@vajhoej.dk> - 2016-06-07 21:53 -0400
        Re: Picking an unused port number a.laforgia@gmail.com - 2016-06-07 00:11 -0700

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