![]() ![]() 71 00 00 00 = SLL ( Linux "cooked" capture encapsulation).65 00 00 00 = Raw IP packets (no layer 2 header).Some of the most common link-layer type values are: ![]() Then all packets in that file should be parsed as Ethernet packets. ![]() The link layer type defines which type of packets the capture file contains.Īs an example, if the link-layer field is “01 00 00 00” in a little endian PCAP file, This value is often “00 00 04 00” (256 kB) or “ff ff 00 00” (65535 bytes), but can in theory be any value except zero. The snap length value is a 32 bit number indicating the maximum packet size that can be stored in the PCAP without truncating the packet data. The timezone and accuracy fields aren’t used in practice, they should therefore be all zeroes. There are a few additional magic number variants, such as “4d 3c b2 a1” used to indicate nanosecond timestamps and FRITZ!Box’s “34 cd b2 a1”, as well as big endian versions of those magic numbers. There is one common exception though, which is when the field values are encoded as big endian rather than little endian.Ī big endian capture file typically starts with these 8 bytes: Timestamp Accuracy (4 bytes) = 00 00 00 00Īs shown above, the first 16 bytes in the PCAP header have fixed values.Referred to as pcap_file_header in the libpcap source code, A PCAP file always starts with a 24 byte header, ![]()
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