Which layer 2 protocol encapsulation type supports synchronous and asynchronous circuis and has built-in security mechanisms?（）

多项选择题Which two options are valid WAN connectivity methods?（）

A.PPP
B.WAP
C.DSL
D.Ethernet
E.L2TPv3

单项选择题At which layer of the OSI model dose PPP perform?（）

A.Layer 3
B.Layer 4
C.Layer 2
D.Layer 5

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

A. L2TP
B. IPsec
C. PPTP
D.RSA

单项选择题which command is used to enable CHAP authentication whit PAP as the fallback method on a serial interface?（）

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

单项选择题Refer to the exhibit.Statements A,B,C,and D of ACL 10 have been entered in the shown order and appled to interface E0 inbound,to prevent all hosts(except those whose addresses are the first and last IP of subnet 172.21.1.128 28) from accessing the network.But as is,the ACL dose not restrict anyone from the network.How can the ACL statements be re-arranged so that the system works as intended?（）

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