ISL frames
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.
ISL length
The length of the ISL field is 26 bytes before the encapsulated Ethernet frame and 4 bytes of ISL CRC after the Ethernet frame.