Which additional routing protocol would you use for the overlay routing between the group members?

You are designing a Group Encrypted Transport virtual private network solution for an existing branch network.

The existing network has the following characteristics:

. 50 remote sites (with an additional 30 remote sites expected over the next 3 years)

. Connectivity between all sites is via Multiprotocol Label Switching Layer 3 virtual private network service from a single provider

. Open Shortest Path First is the routing protocol used between provider edge and customer edge routers

. The customer edge routers will become group members performing the encryption between sites

Which additional routing protocol would you use for the overlay routing between the group members?
A . Open Shortest Path First (with a different process ID)
B . Enhanced Interior Gateway Routing Protocol
C . No additional protocol is necessary.
D . External Border Gateway Protocol
E . Routing Information Protocol Version 2
F . Next Hop Resolution Protocol