ISL is being configured on a Company switch.  Which of the following choices are true regarding  the ISL protocol？ （）

• A、 It can be used between Cisco and non-Cisco switch devices.
• B、 It calculates a new CRC field on top of the existing CRC field.
• C、 It adds 4 bytes of protocol-specific information to the original Ethernet frame.
• D、 It adds 30 bytes of protocol-specific information to the original Ethernet frame.