Network problems

There are a number of things to check if you are experiencing network problems.

When using LU 6.2, make sure that your definitions are consistent throughout the network. For example, if we have increased the RU sizes in your CICS® Transaction Server for z/OS® or Communications Manager definitions, but we have a controller with a small MAXDATA value in its definition, the session might fail if you attempt to send large messages across the network. A symptom of this problem might be that channel negotiation takes place successfully, but the link fails when message transfer occurs.

When using TCP, if your channels are unreliable and your connections break, we can set a KEEPALIVE value for your system or channels. You do this using the SO_KEEPALIVE option to set a system-wide value.

On IBM MQ for z/OS, you also have the following options:

  • Use the Keepalive Interval channel attribute (KAINT) to set channel-specific keepalive values.
  • Use the RCVTIME and RCVTMIN channel initiator parameters.
These options are discussed in Checking that the other end of the channel is still available, and Keepalive Interval (KAINT).


Adopting an MCA

The Adopt MCA function enables IBM MQ to cancel a receiver channel and to start a new one in its place.

For more information about this function, see Adopting an MCA.


Registration time for DDNS

When a group TCP/IP listener is started, it registers with DDNS. But there can be a delay until the address is available to the network. A channel that is started in this period, and which targets the newly registered generic name, fails with an error in communications configuration message. The channel then goes into retry until the name becomes available to the network. The length of the delay is dependent on the name server configuration used.