Cisco IOS is the software used on the vast majority of Cisco Systems routers and current Cisco network switches. As a network administrator, you are required to configure MPLS on Cisco IOS. In such a situation,which three of the following steps are necessary to take?（）
A. Start LDP.
B. Enable CEF switching.
C. Configure conditional label advertising.
D. Enable label switching on frame mode interfaces.
E. disable IP TTL propagation
F. configure conditional label advertising
正确答案：参考A, B, D
