Cisco CCNA mock exam questions sample test – Question 362

.Which statement is true regarding Inter-Switch Link (ISL) frame tagging?

A. ISL uses a native VLAN.
B. ISL works with non-Cisco switches.
C. ISL adds a 26-byte trailer and 4-byte header.
D. The original Ethernet frame is not modified.

Correct Answer: D

Explanation:
With ISL frame tagging, the original Ethernet frame is not modified. ISL encapsulates the original frame by adding a 26-byte header and a 4-byte Cyclic Redundancy Check (CRC)
trailer. The original Ethernet frame is placed between the header and trailer. A normal Ethernet frame can have a maximum size of 1,518 bytes, and therefore adding the header and
trailer size gives an ISL frame a maximum size of 1,548 bytes.
ISL frame tagging does not use the concept of a native VLAN. Instead, Institute of Electrical and Electronics Engineers (IEEE) 802.1q frame tagging uses the native VLAN. Unlike ISL
trunks, where every frame traversing the trunk is tagged with an ISL header and a trailer, 802.1Q trunks allow untagged frames over the native VLAN. An untagged frame does not
carry VLAN identification information in it and is a simple Ethernet frame.
ISL is proprietary to Cisco, and thus does not work with non-Cisco switches.
ISL frame tagging does not add a 26-byte trailer and 4-byte header. It adds a 26-byte header and 4-byte trailer.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Configure and verify Layer 2 protocols
References:
Cisco > Technology Support > LAN Switching > Virtual LANs/VLAN Trunking Protocol (VLANs/VTP) > Design > Design Technotes > Inter-Switch Link and IEEE 802.1Q Frame
Format > Document ID: 17056