Refer to the exhibit. A network engineer configures a GRE tunnel and enters the show Interface tunnel command. What does the output confirm about the configuration?

Question

Exhibits

Options

• AThe keepalive value is modified from the default value.
• BInterface tracking is configured.
• CThe tunnel mode is set to the default.
• DThe physical interface MTU is 1476 bytes.

• A
  3% (1)
• B
  6% (2)
• C
  88% (28)
• D
  3% (1)

Explanation

Explanation

Option C is correct because GRE is the default tunnel mode on Cisco routers, and when no explicit tunnel mode command is configured, the show interface tunnel output will display "Tunnel protocol/transport GRE/IP" - confirming the default GRE over IP mode is in use without any manual configuration.

Why the distractors are wrong:

• Option A is incorrect because keepalive is disabled by default on GRE tunnels; if it were modified, the output would explicitly show a keepalive timer value, which is not indicated here.
• Option B is incorrect because interface tracking (used with IP SLA or HSRP) would require additional configuration commands and would appear separately in routing or tracking outputs, not confirmed by this tunnel interface output alone.
• Option D is incorrect because 1476 bytes is the GRE tunnel's MTU, not the physical interface MTU - the physical interface typically has an MTU of 1500 bytes, and GRE adds a 24-byte overhead, reducing the tunnel MTU to 1476.

Memory Tip: Think "GRE = Default" - on Cisco devices, if you build a tunnel and never specify a mode, it's automatically GRE/IP. Any output showing GRE without explicit configuration confirms the default is active.

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