Refer to the exhibit. Which command must be applied to Router1 to bring the GRE tunnel to an up/up state?

Question

Exhibits

Options

• ARouter1(config)#interface tunnel0
• BRouter1(config-if)#tunnel source GigabitEthernet0/1
• CRouter1(config-if)#tunnel mode gre multipoint
• DRouter1(config-if)#tunnel source Loopback0

• B
  4% (1)
• C
  4% (1)
• D
  92% (24)

Explanation

GRE Tunnel Source Configuration

Option D is correct because the GRE tunnel on Router1 must have a tunnel source that matches the IP address being used as the tunnel endpoint - and based on the exhibit context, Router1's Loopback0 interface holds the correct source IP that Router2's tunnel destination is pointing to. Without a properly matched tunnel source, the tunnel cannot reach an up/up state.

Why the distractors are wrong:

• Option A simply enters interface tunnel0 configuration mode - it's a navigation command, not a solution that fixes the tunnel state.
• Option B configures GigabitEthernet0/1 as the tunnel source, but the exhibit indicates Router2's tunnel destination points to Router1's Loopback0 IP address, not the physical interface - creating a mismatch.
• Option C changes the tunnel mode to mGRE (used in DMVPN), which is unnecessary and incorrect for a standard point-to-point GRE tunnel setup shown in the exhibit.

Memory Tip: Think of it as a "matching handshake" - the tunnel source on one router must match the tunnel destination configured on the other router. When in doubt, check what IP address the remote router is pointing to, and make sure the local router sources from that same address.

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