The following statement about IPSec VPN is correct (multiple choice)

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The following statement about IPSec VPN is correct (multiple choice)
A. If two routers establish IPSec VPN in barbaric mode, the tunnel can be established only after at least four messages are exchanged between two devices
B. Brute mode can support NAT traversal, while main mode does not
C. Two routers can establish OSPF neighbor relationship through IPSec VPN tunnel, and exchange intranet route
D. Two routers set up IPSec VPN through main mode. Starting from the fifth packet (included), the loaded data is often encrypted

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