In the following figure, a GRE tunnel is established between R1 and R2.

Comprehensive and Detailed In-Depth Explanation:

1. GRE Tunnel Configuration Details:

GRE (Generic Routing Encapsulation)is used to encapsulate packets for transmission between two endpoints.

The tunnel is created betweenR1andR2:

R1 Tunnel IP:10.1.1.1

R2 Tunnel IP:10.3.1.1

Source IP of Tunnel:10.0.12.1 (R1)

Destination IP of Tunnel:10.0.12.2 (R2)

The command used: ping -a 10.1.1.1 10.3.1.1

Source IP (Inner IP):10.1.1.1

Destination IP (Inner IP):10.3.1.1

2. GRE Encapsulation Process:

When thepingcommand is executed from R1 to R2 through the GRE tunnel:

Theoriginal ICMP packetwill have:

Source IP:10.1.1.1

Destination IP:10.3.1.1

This ICMP packet (inner packet) will be encapsulated using GRE.

GRE Encapsulation:

Outer IP Header:

Source IP:10.0.12.1 (R1 GE0/0/1 interface)

Destination IP:10.0.12.2 (R2 GE0/0/1 interface)

Inner IP Header:

Source IP:10.1.1.1 (Tunnel0/0/0 on R1)

Destination IP:10.3.1.1 (Tunnel0/0/0 on R2)

Theouter IP headeris used fortunnel routingbetween thephysical interfaces(GE0/0/1).

Theinner IP headerrepresents thelogical tunnel IPsused for communication between R1 and R2.

3. Correct Answer Analysis:

Option A:

Correct.

Theouter IP headeraddresses are10.0.12.1and10.0.12.2, representing thephysical interfaces (GE0/0/1)used to establish the tunnel.

Option C:

Correct.

Theinner IP headeraddresses are10.1.1.1and10.3.1.1, representing thelogical tunnel interfacesused for communication.

4. Why Other Options Are Incorrect:

Option B:

Incorrect.

Thedestination IP in the outer headershould be thepeer physical IP (10.0.12.2), not the tunnel IP (10.3.1.1).

Option D:

Incorrect.

Theinner IP destinationis thetunnel IP (10.3.1.1), not thephysical IP (10.0.12.2).