Binding to a TCP/IP socket or port
 Technote (troubleshooting)
 
Problem(Abstract)
Instructions and general information about TCP/IP® and how to bind to ports when using WebSphere® Application Server for z/OS®.
 
Resolving the problem

Basic Information:
  1. The term stack relates to a particular TCP/IP address space on an MVS system. If you had "2 stacks" you would have two TCP/IP address spaces on that system.
  2. Each stack can and usually does have multiple IP addresses defined to it.
  3. A Domain Name Server (DNS ) converts a host name (plpsc.pok.ibm.com) to a real IP address that TCP/IP uses to find your system
  4. You can have one IP address mapped to multiple HOSTNAMES or one HOSTNAME mapped to multiple IP addresses.


This is a general description of the process of getting a TCP/IP socket:
  1. Connect to a socket (or PORT) using a TCP/IP socket( ) call. This returns an object that identifies all of the IP addresses on all of the stacks in the system.
  2. A TCP/IP bind() is done. On the bind() you can specify the particular IP address you want to use or bind to. If you use a NULL IP address or 0.0.0.0., you bind to every IP address on every stack.
  3. A TCP/IP Listen() is performed. This makes your system available to receive TCP/IP traffic on all of these IP addresses for the specified PORT or socket.

This information was obtained while trying to understand how we setup the ND to NodeAgent discovery port and changes made in APAR PQ77226:
  1. PQ77226 not only added a parameter to turn off multi home, it also resolved some problems with configuring and using the socket.
  2. Before this APAR, the Node Agent listened on all ports; however, when a request came in, it used the IP address on the request to get the HOSTNAME associated with the request. That is compared to the configured HOSTNAME to see if this request is for us. If the same IP address mapped to multiple HOSTNAMES, we might get the wrong hostname back and the request will be denied.
  3. After PQ77226. we still listen on all IP addresses but, we use the configured HOSTNAME to see if any IP addresses associated with that HOSTNAME match the request.
 
 
 


Document Information


Current web document: swg21170758.html
Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server for z/OS > Install
Operating system(s): z/OS
Software version: 5.0
Software edition:
Reference #: 1170758
IBM Group: Software Group
Modified date: Jun 3, 2004