The trace process

Trace data is collected as IP packets enter or leave TCP/IP. The actual collection occurs within the device drivers of TCP/IP, which capture the data that is received from or sent to the network.

Packets that are captured have extra information added to them before they are stored. This extra information is used during the formatting of the packets. The captured data reflects exactly what the network sees. For example, the trace contains the constituent packets of a fragmented packet exactly as they are received or sent.

The selection criteria for choosing packets to trace are specified through the PKTTRACE statement for the TCP/IP address space. See z/OS Communications Server: IP System Administrator's Commands for more information about the PKTTRACE statement and subcommand.

The PKTTRACE statement and subcommand are applied to device links that are defined in the TCP/IP address space through the LINK statement. Figure 1 illustrates the overall control and data flow in the IP packet tracing facility.

Figure 1. Control and data flow in the IP packet tracing facility
Diagram that shows the data flow in this sequence: TCPIP profile/VARY TCP/IP, TCPIP address space, TCPIP data space, CTRACE data set, IPCS format program, and trace report.
Parent topic: Packet trace (SYSTCPDA) for TCP/IP stacks