You are bringing up a new Cisco Catalyst switch, and wish to connect it via a trunk to another switch from a different vendor, which uses the IEEE?

A. Switch(config)# switchport trunk encapsulation isl
B. Switch(config)# switchport trunk encapsulation ietf
C. Switch(config-if)# switchport trunk encapsulation isl
D. Switch(config-if)# switchport trunk encapsulation ietf
E. Switch(config-if)# switchport trunk encapsulation dot1q

Answer: E

Explanation: The only real choices for setting up switching trunks are ISL and
802.1Q. ISL is Cisco proprietary, while 802.1Q uses the IEEE defined standard for
trunking between switches. To configure the 802.1Q standard, the keyword "dot1q" is used in Cisco switches.

Incorrect Answers:
A, B, D. These are not valid options in a Cisco switch.
C. ISL is a Cisco proprietary method for setting up trunks, and will only work between Cisco switches.