A.IPSec VPN
B.SSL VPN
C.port security
D.port security with statically configured MAC addresses
E.private VLANs

A. Make HSRP track interfaces between the edge and core routers.
B. Replace HSRP with GLBP.  用GLBP替換HSRP
C. Add crossed intrasite links： R1-R4， R2-R3， R5-R8， and R6-R7.
D. Make R3 and R8 have lower HSRP priority than R1 and R7.
E. Replace HSRP with VRRP

A.root guard
B.loop guard
C.BPDU guard
D.UDLD
E.BPDU skew detection

A. Because Frame Relay IETF encapsulation is only configurable at interface level， you must use IETF encapsulation on all routers.
B. This is not a possible scenario. A dedicated Frame Relay link to RemoteB is mandatory at the central office.
C. The router at RemoteB must be replaced by a Cisco router.
D. Use Frame Relay IETF encapsulation on a per-VC basis on the central office router.
E. There is a problem in the Frame Relay cloud， because Cisco routers are compatible with IETF Frame Relay.

A.ip verify unicast source reachable-via any
B.ip verify unicast reverse-path
C.ip verify unicast reverse-path loose
D.ip verify unicast reverse-path strict