Custom dissector for LLC Payload in Lua

Hi,

I'd like to preface this by stating that this is my first time making a dissector in Lua (or really working in Wireshark for that matter) so if anything is unclear I'd be more than happy to clarify. My goal is to make a custom dissector for a protocol on top of SNAP LLC frames. Since the protocol info is currently dissected as "data," it seems that a chained dissector is appropriate. Using https://delog.wordpress.com/2010/09/27/create-a-wireshark-dissector-in-lua/ as a guide, I have created the following:

iiot = Proto("myproto", "My Protocol")
local f_type = ProtoField.new("Type Value", "myproto.type",  ftypes.UINT16, nil, base.HEX)
local f_data = ProtoField.string("Data", "myproto.data", FT_STRING)
iiot.fields = { f_type, f_data }
function iiot.dissector(buf, pkt, root)
 pkt.cols.protocol:set("IIOT")

 local pktlen_remaining = buf:reported_length_remaining()

 local tree = root:add(iiot, buf:range(0, pktlen_remaining))

 tree:add(f_type, buf:range(0, 2))

 local typeid = buf:range(0, 2)
 pkt.cols.info:set("(".. typeid ..")")

 pktlen_remaining = pktlen_remaining - 2

 tree:add(f_data, buf:range(2, pktlen_remaining))

 local data = buf:range(2, pktlen_remaining)
 pkt.cols.info:set("(".. data ..")")

end
local llc_dissector_table = DissectorTable.get("llc.dsap")
dissector = llc_dissector_table:get_dissector(170)
llc_dissector_table:add(170, iiot)

I suppose my question is two-fold. At present, my dissector loads and I can filter by “myiiot”. However, I am unable to dissect my packets using the “Decode As…” window. Since my packets are 0xaa SNAP, shouldn’t they automatically be dissected by my script? Is there a way to do this manually assuming the code is correct? Apologies if I am missing something obvious.

edit: Here is a CloudShark link for the capture https://www.cloudshark.org/captures/fef0e7fd73d3