-pcap Network Type 276 Unknown Or Unsupported- //free\\ -

(also known as DLT_ETHERNET_MPACKET ). This is a relatively rare link-layer header type used for packet aggregation —specifically, encapsulating multiple Ethernet frames into a single PCAP record. Your current tool (likely an older version of Wireshark, TShark, or a custom analyzer) does not recognize this DLT (Data Link Type).

: The LINKTYPE_LINUX_SLL2 support was added to tcpdump during its development in 2018. If you're on an older system, updating tcpdump via your system's backports or compiling from source is necessary. -pcap network type 276 unknown or unsupported-

tshark --version | grep "with libpcap" # or ldd `which tcpdump` | grep pcap rpcinfo -p | grep -i pcap # alternative (also known as DLT_ETHERNET_MPACKET )

The core issue is not the number itself, but the fact that your current libpcap version . : The LINKTYPE_LINUX_SLL2 support was added to tcpdump

Most network captures use standard link types like Ethernet (Type 1) or IEEE 802.11 (Type 105). Type 276 is a proprietary Cisco format. When a capture is taken on a Cisco device using tools like ethanalyzer or "Cisco Logic" captures, the resulting .pcap or .pcapng file contains metadata headers that standard tools don't recognize.