单项选择题
A. denial of service
B. brute force
C. reconnaissance
D. Trojan horse
单项选择题 What is the default routing update period for RIPv2?（）
单项选择题 An administrator issues the command ping 127.0.0.1 from the command line prompt on a PC. If a reply is received, what does this confirm?（）
单项选择题 How does using the service password encryption command on a router provide additional security? （）