The frame decoder recognizes an ISL-encapsulated frame if the frame being analyzed has a
destination MAC address equal to 01:00:0C:00:00:0X or 03:00:0C:00:00:0X.
Note: A single packet cannot be recognized both as an ISL-encapsulated
frame and a CFP-encapsulated frame. For packets with both encapsulations, the
outermost encapsulation is decoded and the inner layer 2 packet is decoded as EtherII
(for recognized CFP encapsulation) or SNAP (for recognized ISL encapsulation), and
further decoding is stopped.
The length of the ISL field is 26 bytes before
the encapsulated Ethernet frame and 4 bytes of ISL CRC after the Ethernet frame.