The following configuration exists on a router on one end of an IPv6 tunnel. Although the configuration added so far is correct, the configuration is incomplete. Which type of tunnel is most likely to be intended by the network engineer？（） interface loopback 1 ip address 192.168.1.1 255.255.255.255 interface tunnel 2 ipv6 address 2002:C0A8:10 1::1/64 tunnel source loopback 1

• A、Automatic 6to4
• B、Manually configured tunnel
• C、ISATAP
• D、GRE