I/O trace

The I/O trace shows requests and responses that flow between VTAM® and network nodes. You can trace I/O activity for any of the following types of nodes:

Application program
Physical unit
Logical unit
SNA cluster controller
NCP
SSCP
Host physical unit
Host as an intermediate routing node
Channel attachment major node
Cross-domain resource
Cross-domain resource manager
RTP pipe
TRLE
Restriction: I/O trace is not supported for a TRLE that represents an IBM 10GbE RoCE Express interface.

The maximum I/O trace record length is 272 bytes.

Note:

If you want to trace a session between an LU and an application program, you must start the trace at the host where the application program resides.
I/O trace records are not recorded for conversation level data exchanged between two VTAM/APPC applications residing on the same host and using the APPCCMD macroinstruction interface to communicate.
I/O trace provides packet tracing capability for OSA-Express QDIO and HiperSockets™ data devices because CCW trace does not exist for these devices. Packet trace for OSA-Express QDIO and HiperSockets will appear as ODPK records in the external VIT. A length field is provided on the MODIFY TRACE command for OSA-Express QDIO and HiperSockets devices to override the existing 272-byte trace limit for I/O trace.
Do not enable I/O trace for an OSA-Express2 or later data device that is used to capture OSA-Express network traffic analyzer trace data. The VARY TCPIP,,OSAENTA command described in z/OS Communications Server: IP Diagnosis Guide has its own ability to filter, capture, and format this data. If I/O trace is enabled for a data device used for capturing trace data, only the first 28 bytes of each packet are traced.
You must use a combination of the TCP/IP packet trace facility and VTAM internal trace (VIT) records to analyze Shared Memory Communications - RDMA (SMC-R) link traffic. The RPST records in the VIT represent data being sent outbound by using SMC-R communications. The RPLR records in the VIT represent data arriving inbound by using SMC-R communications. For information about the TCP/IP packet trace, see z/OS Communications Server: IP Programmer's Guide and Reference.