You work as a network engineer, do you know an IPsec tunnel is negotiated within the protection of which type of tunnel?

A.
GRE tunnel

B.
L2TP tunnel

C.
L2F tunnel

D.
ISAKMP tunnel

Explanation:
During IKE Phase 1, a secure ISAKMP session is established, using either main
mode or aggressive mode. During IKE Phase 1, the IPsec endpoints establish
transform sets (that is, a collection of encryption and authentication protocols), hash
methods, and other parameters needed to establish a secure ISAKMP session
(sometimes called an ISAKMP tunnel or an IKE Phase 1 tunnel).