350-401 Question #534: Real Exam Question with Answer & Explanation

Question

An engineer is configuring a GRE tunnel interface in the default mode. The engineer has assigned an IPv4 address on the tunnel and sourced the tunnel from an Ethernet interface. Which option also is required on the tunnel interface before it is operational?

Options

• A(config-if)#tunnel destination <ip address>
• B(config-if)#keepalive <seconds retries>
• C(config-if)#ip mtu <value>
• D(config-if)#ip tcp adjust-mss <value>

Explanation

To make a GRE tunnel operational after assigning an IPv4 address and sourcing it from an interface, the tunnel's destination IP address must also be configured.

Common mistakes.

• B. The keepalive command is optional and used for monitoring tunnel interface status, but it's not strictly required for the tunnel to become operational.
• C. The ip mtu command adjusts the Maximum Transmission Unit for the tunnel, which can prevent fragmentation issues but is not a fundamental requirement for the tunnel's basic operational state.
• D. The ip tcp adjust-mss command is used to prevent TCP reassembly issues by modifying the TCP Maximum Segment Size, but it is not essential for the GRE tunnel itself to be operational.

Concept tested. GRE tunnel destination configuration

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/configuration/xe-3s/ir-gre-tunnels-xe-3s-book/ir-gre-tunnel-xe.html

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