Troubleshooting network problems

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

Procedure

  • When using LU 6.2, make sure that your definitions are consistent throughout the network.
    For example, if you have increased the RU sizes in your CICS® Transaction Server for z/OS® or Communications Manager definitions, but you 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, try setting a KEEPALIVE value for your system or channels.
    You do this using the SO_KEEPALIVE option to set a system-wide value.
    [z/OS]On 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.
    For more information, see Checking that the other end of the channel is still available, and Keepalive Interval (KAINT).
    Note: 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.
  • If the receiver channel has been left in a 'communications receive' state after the channel lost contact, check whether user intervention is needed to address the problem.
    If a channel loses contact, the receiver channel can be left in a 'communications receive' state. When communications are re-established the sender channel attempts to reconnect. If the remote queue manager finds that the receiver channel is already running it does not allow another version of the same receiver channel to start. This problem requires user intervention to rectify the problem or the use of system keepalive.

    The Adopt MCA function solves the problem automatically. It enables IBM® MQ to cancel a receiver channel and to start a new one in its place.