To securely transport EIGRP traffic, a network administrator will build VPNs between sites. What
is the best method to accomplish the transport of EIGRP traffic?

A.
IPSec in tunnel mode

B.
IPSec in transport mode

C.
GRE with IPSec in transport mode

D.
GRE with IPSec in tunnel mode

Explanation:
The right answer is GRE with IPSec in tunnel mode.
In Designing Cisco Network Service Architectures (ARCH) is explains, that in order to transport
EIGRP routing updates, it is GRE over IPsec tunnel. See page 404.