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Custom dissector for ethertype link layer and IP protocol

This is how you can replace the default dissector for the IP protocol

local dissector_table = DissectorTable.get("ethertype")
if dissector_table ~= nil then
    dissector_table:add(0x800, p_myproto)
end

If you have a capture file with a different link layer start at How to Dissect Anything.

To test your dissector, this is how you can write binary representation of a message to pcap

od -Ax -tx1 -v myproto.bin > myproto.hex
text2pcap -l 147 myproto.hex myproto.pcap

Valid values of link type specified using option -l are in the range 147 to 162.

Next, customize the DLT_USER protocol preferences, so that your dissector gets invoked for link type 147

DLT_USER protocol preference

You can do the same thing from a Lua dissector

local wtap_encap_table = DissectorTable.get("wtap_encap")
wtap_encap_table:add(wtap.USER0, p_myproto)