NSE4 · Question #90
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
The correct answer is B. The FortiGate device forwards received spanning tree messages.. 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.
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.
How the community answered
(20 responses)- A5% (1)
- B90% (18)
- C5% (1)
Why each option
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.
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.
In transparent mode, when `stp-forward enable` is configured on an interface, the FortiGate acts as a Layer 2 bridge and is instructed to simply forward any received Spanning Tree Protocol (STP) BPDU frames between connected switches without processing or originating its own BPDUs. This allows the switches on either side of the FortiGate to maintain their STP topology correctly.
By forwarding BPDUs, the FortiGate allows the switches to correctly build a loop-free topology, thus *preventing* Layer 2 loops, rather than causing them.
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
Source: https://docs.fortinet.com/document/fortigate/7.4.0/administration-guide/546452/bridging-and-layer-2-switching
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