Which three techniques should be used to secure management protocols？（）

• A、Configure SNMP with only read-only community strings.
• B、Encrypt TFTP and syslog traffic in an IPSec tunnel.
• C、Implement RFC 3704 filtering at the perimeter router when allowing syslog access from devices on the outside of a firewall.
• D、Synchronize the NTP master clock with an Internet atomic clock.
• E、Use SNMP version 2.
• F、Use TFTP version 3 or above because these versions support a cryptographic authentication mechanism between peers.