单项选择题 Which site-to-site VPN solution allows Cisco routers, PIX Firewalls, and Cisco hardware clients to act as remote VPN clients in order to receive predefined security policies and configuration parameters from the VPN headend at the central site?（）

单项选择题 When designing the WAN module within the enterprise edge, which document is used to specify the connectivity and performance agreements with the service provider?（）

单项选择题 You are the network consultant from Cisco.com. Please point out the reason that STP required when VLANs do not span access layer switches.（）