Dump the compiled packet-matching code in a human readable form of form in a form of code. The code:loads the 2-byte big-endian quantity at an offset of 12 from the beginning of the packet – which, on an Ethernet packet, is the type/length field in the Ethernet header. If it’s not equal, it jumps to instruction 8, meaning “reject this packet” (i.e., it rejects all packets that don’t have a source IP address of 162.129129.225.192, or “centernet.jhuccp.org””]
Source: https://taosecurity.blogspot.com/2004/09/understanding-tcpdumps-d-option-have.html