pkt

%% Copyright (c) 2009-2016, Michael Santos <michael.santos@gmail.com>
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%% IEEE 802.1Q, 802.1ad (802.1q QinQ)
-module(pkt_802_1q).

-include("pkt_802_1q.hrl").

-export([codec/1]).

% See: https://en.wikipedia.org/wiki/IEEE_802.1ad
%
% The 802.1q 4-byte tag is inserted into the frame between the source
% MAC and the original tag:
%
%   Original frame:
%       <<Dhost:6/bytes, Shost:6/bytes, EtherType:16, Payload/binary>>
%
%   With 802.1q tag:
%       <<Dhost:6/bytes, Shost:6/bytes,
%           16#81, 16#00, Prio:3, CFI:1, VID:12,
%           EtherType:16, Payload/binary>>
%
%   802.1ad (802.1QinQ) tag:
%       <<Dhost:6/bytes, Shost:6/bytes,
%           16#88, 16#a8, Prio:3, CFI:1, VID:12,
%           16#81, 16#00, Prio:3, CFI:1, VID:12,
%           EtherType:16, Payload/binary>>
%
% The original ethernet type tag is replaced with the 802.1q TPID. The
% inner 802.1q header (tag 2 or C-TAG) is set to the original ethertype.
%
codec(<<Prio:3, CFI:1, VID:12, Type:16, Payload/binary>>) ->
    {#'802.1q'{
        prio = Prio,
        cfi = CFI,
        vid = VID,
        type = Type
    }, Payload};
codec(#'802.1q'{prio = Prio, cfi = CFI, vid = VID, type = Type}) ->
    <<Prio:3, CFI:1, VID:12, Type:16>>.