NSE4 Question #90: Real Exam Question with Answer & Explanation

Question

Examine the following spanning tree configuration on a FortiGate in transparent mode: config system interface edit <interface name> set stp-forward enable end Which statement is correct for the above configuration?

Options

• AThe FortiGate participates in spanning tree.
• BThe FortiGate device forwards received spanning tree messages.
• CEthernet layer-2 loops are likely to occur.
• DThe FortiGate generates spanning tree BPDU frames.

Explanation

In transparent mode, enabling stp-forward on a FortiGate interface configures the device to pass through Spanning Tree Protocol (STP) Bridge Protocol Data Units (BPDUs) between connected switches.

Common mistakes.

• A. The stp-forward enable setting in transparent mode specifically means the FortiGate does not participate in the spanning tree algorithm itself; it only forwards the BPDUs.
• C. By forwarding BPDUs, the FortiGate allows the switches to correctly build a loop-free topology, thus preventing Layer 2 loops, rather than causing them.
• D. The FortiGate in transparent mode with stp-forward enable does not generate its own BPDU frames; it only passes through BPDUs from other switches.

Concept tested. FortiGate transparent mode STP forwarding

Reference. https://docs.fortinet.com/document/fortigate/7.4.0/administration-guide/546452/bridging-and-layer-2-switching

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