editcap -T 1 broken_type276.pcap fixed_ethernet.pcap If the packets are raw IP (no header, Type 101):
276, "CUSTOM_MY_PROTO", DLT_CUSTOM , Recompile and install libpcap. This is overkill for most users. A security team was auditing a fleet of medical IoT devices (insulin pumps) that communicated via 802.15.4 (ZigBee). They captured traffic using a dedicated USB dongle which wrote pcap files with DLT 276 (mapped to DLT_IEEE802_15_4_TAP ). When they transferred the file to their central Linux analysis server (running RHEL 7 with an older libpcap), they received the error: -pcap network type 276 unknown or unsupported-
You run a command—perhaps a custom tcpdump filter, a tcpslice extraction, or a specialized fuzzer—and the terminal spits out: editcap -T 1 broken_type276
-pcap network type 276 unknown or unsupported- Type 101): 276