Correct Answer : Option (C) : Layer 3
Explanation : IPSec is a set of protocols used to provide authentication, data integrity and confidentiality between two machines in an IP network. It operates in the network layer.
Correct Answer : Option (A) : DUAL
Explanation : EIGRP uses the DUAL algorithm for finding shortest path. DUAL stands for diffusing update algorithm and it is used to prevent routing loops by recalculating routes globally.
Correct Answer : Option (B) : 170
Explanation : Routers use the metric of administrative distance to select the best path when there are different routes to the same destination from two different routing protocols as it is a measure of reliability of routing protocols. Administrative distance for external EIGRP is 170.