A network designer has provisioned a router to use IPsec to encrypt the traffic over a GRE tunnel going to a web server at a remote location. From the router, the network designer can ping the web server, although the users in the office comment that they are unable to reach it. (Note: The DF bit is not set.) Which aspect should be changed in the design of the virtual connection?
A. IP addresses of the GRE tunnel endpoints
B. IPsec configuration
C. MTU size on the GRE tunnel
D. encapsulation of the GRE tunnel
