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Problem(Abstract) |
Instructions and general information about TCP/IP® and how
to bind to ports when using WebSphere® Application Server for z/OS®. |
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Resolving the
problem |
Basic Information:
- 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.
- Each stack can and usually does have multiple IP addresses defined to
it.
- 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
- 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:
- 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.
- 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.
- 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:
- PQ77226 not only added a parameter to turn off multi home, it also
resolved some problems with configuring and using the socket.
- 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.
- 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.
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