What is a Port ?

A port is just a interface (or for example we can imagine our telephone socket on the phone) between two computers or two software  programs. So  if  two computers want  to talk to each other, each  of them should communicate  through  a  port. If  two  software  programs want to talk  with  each  other, each of them should talk through a  port .To know more about  hardware  ports please check.  Hardware port .

A  DBA should mostly  be concerned with  software  ports. This  software  port  is  like a virtual (no physical shape) connection so  software  programs talk with  each other. The  two  well  known  ports  used by  majority  of  software  programs are  the TCP and UDP ports.

During  installation , Oracle  Universal  Installer  assigns  port  numbers  to components from  a  set  of default port numbers. Many Oracle Database components and services use ports. As  an  administrator ,  it is  important  to  know  the  port  numbers  used  by these services, and  to  make  sure  that  the  same  port number  is  not   used  by  two  services  on  our   host .

Most  port numbers are assigned during installation. Every  component and service has an allotted  port range, which  is the set  of  port  numbers  Oracle  Database  attempts to  use when  assigning a  port . Oracle  Database starts  with  the  lowest  number  in  the  range  and  performs  the  following  checks:

I.) Is  the  port  used  by  another  Oracle  Database  installation  on  the  host?
 The  installation  may  be  up or down at  the  time; Oracle  Database  can  still  detect  if  the port  is  used.

II.) Is  the  port  used  by a  process  that  is  currently  running?
This  could be  any  process  on  the  host, even  a  non-Oracle  Database  process.

If  the answer  to  any  of  the  preceding  questions  is  yes, Oracle  Database  moves  to  the  next  highest port in  the  allotted  port  range  and continues  checking  until  it   finds a  free port.

If  we change a port number, it is not updated in the portlist.ini file, so we can only rely on this file immediately after installation. if we want to see all the different port numbers click on Different Port Numbers.

When   we  install oracle enterprise manager on a  server ,oracle automatically assigns some  port numbers to it. So we can open the database control in 10g by using a link like http://servername:1158.com. Here 1158  is the port number.

So, in  this  way  different  oracle  components  uses  different port numbers and  hence we should  know what  a  port  is. Sometimes  problems  would  become because  the  port  is  blocked  by  a  firewall or  the unix administrator has not  configured the port correctly. So in those cases we have to speak to the administrator  to  see  that  the  port  is  configured  correctly.

Enjoy    :-)