You are using an older version of Wireshark or tcpdump that predates the addition of the SCLP link type.
In the world of packet capture, every file has a "Linktype" or "Data Link Type" (DLT) field that tells the software how to interpret the data following the header. corresponds to LINKTYPE_SCLP . -pcap network type 276 unknown or unsupported-
The simplest solution is often the most effective. Link Type 276 support has been added to more recent versions of the libpcap library and Wireshark. You are using an older version of Wireshark
The error isn't a sign of a broken file, but rather a compatibility gap between IBM Mainframe protocols and standard networking tools. Updating your software to the latest version is the 90% solution. If you are working in a specialized enterprise environment, you may need to consult IBM-specific documentation for the appropriate dissector plugins. The simplest solution is often the most effective