The number 276 does not appear in the standard dlt.h (data link types) from libpcap 1.9 or 1.10. However, it has appeared in specific contexts.

I encountered this error with a trace from a using a proprietary driver.

The error is an indication that your packet capture toolchain has encountered a rare or custom link-layer header type. While intimidating at first, the resolution is straightforward: identify the true nature of type 276 (NFLOG, custom wireless, or corruption) and either convert to a standard type (Ethernet or SLL) or install the necessary parser.

Checking this file on a different system yields unknown network type 276 .

(from tcpreplay):

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