Which statement correctly describes IPsec VPN backup technology？（）

• A、The cypto isakmp keepalive command is used to configure the Stateful Switchover （SSO）protocol
• B、Reverse Route Injection （RRI） is configured on at the remote site to inject the central sitenetworks
• C、Each Hot Standby Routing Protocol （HSRP） standby group has two well-known MACaddresses and a virtual IP address
• D、The cypto isakmp keepalive command is used to configure stateless failover