What is the command sequence to configure a GRE tunnel interface on a Cisco IOS router?

What is the command sequence to configure a GRE tunnel interface on a Cisco IOS router?

• R4(config)# interface tunnel0 R4(config-if)# ip address 172.16.99.2 255.255.255.0 R4(config-if)# tunnel source GigabitEthernet 0/0
• R4(config)# interface tunnel0 R4(config-if)# ip address 172.16.99.2 255.255.255.0 R4(config-if)# tunnel source interface GigabitEthernet 0/0 R4(config-if)# tunnel destination 10.10.1.1
• R4(config)# interface tunnel0 R4(config-if)# ip address 172.16.99.2 255.255.255.0 R4(config-if)# tunnel source 10.10.3.2 R4(config-if)# tunnel destination 10.10.1.1
• R4(config)# interface tunnel0 R4(config-if)# tunnel source 10.10.3.2 R4(config-if)# tunnel destination 10.10.1.1

Explanation: A minimum Generic Routing Encapsulation (GRE) tunnel configuration requires three core components: a tunnel interface with its own IP subnet, a tunnel source address, and a tunnel destination address.

The configuration sequence involves the following steps:

1. Create the interface: Enter interface configuration mode using the interface tunnel command followed by an ID number.
2. Assign an IP address: Configure an IP address and subnet mask for the tunnel interface to provide connectivity across the logical link.
3. Define the source: Specify the local IP address (or physical interface) that will serve as the origin for the encapsulated packets.
4. Define the destination: Specify the IP address of the remote peer where the tunnel will terminate.

The sources emphasize that the tunnel source and destination must be symmetrical and reachable between the two routers for the line protocol to come "up". In the specific example for router R4, the source is its own physical interface (10.10.3.2) and the destination is the far-end router R1 (10.10.1.1).

Related exam: Modules 17 – 20: Checkpoint Exam: Virtualization and Network Services Answers (CCNP ENCOR v9)