单项选择题
At which layer of the OSI model is RSTP used to prevent loops?（）
A. data link B. network C. physical D. transport
单项选择题 Which IPsec security protocol should be used when confidentiality is required?（）
单项选择题 which command allows you to verify the encapsulation type CISCO OR IETF for a frame relay link?（）
单项选择题 What is the alternative notation for the IPV6 address B514:82C3:0000:0000:0029:EC7A:0000:EC72?（）
