Which three statements are true of GRE tunnels? (Choose three.)
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A. B. C. D. E.ACE
For proper tunnel operations, this route must resolve to the physical next hop in the end-to-end communications path and should never use a recursive route. The tunnel endpoints also need a route with the tunnel interface as the next hop to direct traffic destined to the remote subnet into the tunnel. The intermediary devices, located in the forwarding path between the tunnel endpoints, must also be able to route each of the tunnel endpoints.
Sure, here's a detailed explanation for each statement:
A. The local tunnel endpoint must have a valid route to the remote endpoint: This statement is true. In order to establish a GRE tunnel, the local endpoint must know how to reach the remote endpoint. This is typically accomplished through the use of a static route or a dynamic routing protocol such as OSPF or BGP.
B. GRE tunnels must authenticate at both ends of the tunnel: This statement is false. While it is possible to configure authentication on a GRE tunnel, it is not a requirement. If authentication is used, it can be configured on one or both ends of the tunnel.
C. Tunnel endpoints must have a route that directs traffic into a tunnel: This statement is true. In order for traffic to be sent through a GRE tunnel, there must be a route that directs the traffic into the tunnel. This is typically accomplished through the use of a static route or a dynamic routing protocol.
D. The gr interface can only route packets that are IP protocol packets: This statement is true. The gr interface is a virtual interface that is created when a GRE tunnel is configured. It is used to route packets between the tunnel endpoints. However, the gr interface can only route IP protocol packets.
E. All intermediary devices must have a route to the tunnel endpoints: This statement is true. In order for traffic to be successfully transmitted through a GRE tunnel, all intermediary devices must have a route to the tunnel endpoints. This can be accomplished through the use of static routes or a dynamic routing protocol.