Which protocol is an open standard protocol framework that is commonly used in VPNs,to provid secure end-to-end communication?（）

A.(config-if)#authentication ppp chap fallback ppp
B.(config-if)#authentication ppp chap pap
C.(config-if)#ppp authentication chap pap
D.(config-if)#ppp authentication chap fallback ppp

A.CDBA
B.DBAC
C.ACDB
D.BADC

A.A DHCP client uses a ping to detect address conflicts.(ARP)
B.A DHCP server uses a gratuitous ARP to detect DHCP clients.
C.A DHCP client uses a gratuitous ARP to detect a DHCP server.
D.If an address conflict is detected, the address is removed from the pool and an administrator must resolve the conflict.
E.If an address conflict is detected, the address removed from the pool for an amount of time configurable by the administrator.
F.If an address conflict is detected, the address is removed from the pool and will not be reused until server is rebooted.