Free Fortinet NSE5_FSW_AD-7.6 Practice Exam with Questions & Answers | Set: 4

Tail-drop mode is a congestion management technique used in network devices, including FortiSwitches, to handle congestion on network ports:

Tail-Drop Mode (A):

Behavior:When a queue reaches its maximum capacity on a congested port, tail-drop mode simply drops any incoming packets that arrive after the buffer is full. This continues until the congestion is alleviated and there is space in the queue to accommodate new packets.

Application:This is a straightforward approach used when the device’s buffer allocated to the port becomes full due to sustained high traffic, preventing buffer overflow and maintaining system stability.

According to theFortiSwitchOS 7.6 Administration GuideandFortiOS 7.6 FortiLink Guide, the processing of Ethernet frames on a managed FortiSwitch port depends on whether the frame is tagged or untagged upon arrival (ingress) and how the port's VLAN membership is defined.

In the provided exhibit,port1is configured with set vlan "IP_Phone" (VLAN 20) as itsnative VLAN. By definition, the native VLAN handles untagged traffic; any untagged frame arriving at the port is assigned to VLAN 20, and any egress traffic from VLAN 20 is sent out of the port without a tag. However, the scenario specifically states that theIP phone tags its traffic with VLAN ID 20.

When a FortiSwitch receives atagged frame, it checks the VLAN ID against theallowed-vlanslist configured on that port. Although VLAN 20 is the native VLAN, the exhibit shows that the port has been explicitly configured with set allowed-vlans "quarantine". This creates a restrictive filter that permits only tagged frames belonging to the "quarantine" VLAN to enter or exit the port. Because VLAN 20 (IP_Phone) is not present in the allowed-vlans list, the switch drops the tagged frames from the IP phone during ingress processing.

To resolve this, the administrator must modify theFortiSwitch port configurationby adding VLAN 20 to the allowed_vlans list (e.g., set allowed-vlans "quarantine" "IP_Phone" or set allowed-vlans-all enable). This ensures that the switch recognizes and permits tagged traffic for VLAN 20 on that physical interface. Option B is incorrect because l2forward is a Layer 3 interface setting on the FortiGate and does not address the physical port's ingress filtering logic on the switch. Disabling the edge_port (Option D) relates to Spanning Tree Protocol (STP) convergence and would not impact VLAN tag filtering.

According to theFortiSwitchOS 7.6 Administration Guideand theFortiSwitch 7.6 Study Guide, Multichassis Link Aggregation (MCLAG) and standard Link Aggregation Groups (LAG) are designed to provide link-level and node-level redundancy while presenting a simplified logical view to the Spanning Tree Protocol (STP).

In the provided topology:

Logical Switch View (Option D):Switch 1 and Switch 2 are configured asMCLAG peersconnected via an Inter-Chassis Link (ICL). From the perspective of downstream devices and STP, these two physical switches act as a single logical entity. This prevents STP from seeing a loop between the two switches and the downstream Switch 3, as the redundant physical paths are bundled into a single logical MCLAG trunk.

Logical Interface View (Option B):The exhibit shows Switch 4 connected to Switch 3 via two physical links bundled into aLAG, and Switch 3 connected to the MCLAG peers via split links. In both cases, STP treats the aggregated physical links as asingle logical interface. Because the multiple physical paths are managed by the Link Aggregation Control Protocol (LACP) as one trunk, STP does not block individual ports to prevent loops; instead, it sees one high-bandwidth path.

Regarding the incorrect options:Option Ais false because Switch 3 is an MCLAGclient, not a peer in the group.Option Cis incorrect because Switch 3 and Switch 4 are separate physical and logical nodes; they are not seen as a single client entity by the core.