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Zorluk: ZorSwitching Concepts and VLANs

A network technician is auditing an enterprise Layer 2 campus network consisting of three interconnected switches: Switch-Alpha, Switch-Beta, and Switch-Gamma. The Spanning Tree Protocol (STP) bridge priorities are configured as follows: Switch-Alpha is set to 4096, Switch-Beta is set to 32768, and Switch-Gamma is set to 16384. Additionally, an IEEE 802.1Q trunk link between Switch-Alpha and Switch-Beta has a native VLAN mismatch (configured for VLAN 10 on Switch-Alpha and VLAN 1 on Switch-Beta). Hosts belonging to VLAN 20 are connected across Switch-Beta and Switch-Gamma, with no Layer 3 routing device present on the network. Which TWO of the following statements accurately describe the behavior and operational state of this switching environment?

  1. Switch-Alpha will be elected as the Spanning Tree Protocol (STP) root bridge because it possesses the lowest numerical priority value.Cevap
  2. Untagged frames sent from VLAN 10 on Switch-Alpha will be processed into VLAN 1 upon arrival at Switch-Beta, leading to cross-VLAN traffic leakage.Cevap
  3. C
    Hosts on VLAN 20 connected to Switch-Beta can communicate directly with hosts on VLAN 10 connected to Switch-Gamma without a Layer 3 device.
  4. D
    Switch-Beta will be elected as the STP root bridge because it has the highest numerical priority value.
  5. E
    When frames travel across trunk links on VLAN 20, the switch strips the Layer 2 Ethernet header and encapsulates the payload into a Layer 3 IP packet.

Cevap

The two correct statements are: Switch-Alpha will be elected as the Spanning Tree Protocol (STP) root bridge because it possesses the lowest numerical priority value, and untagged frames sent from VLAN 10 on Switch-Alpha will be processed into VLAN 1 upon arrival at Switch-Beta, leading to cross-VLAN traffic leakage.
Switch-Alpha is elected as the STP root bridge because STP root election prioritizes the lowest numerical bridge priority value (4096 < 16384 < 32768). Furthermore, 802.1Q trunking sends frames belonging to the native VLAN untagged across the link; when Switch-Alpha sends untagged VLAN 10 traffic, Switch-Beta receives it untagged and implicitly assigns it to its own native VLAN (VLAN 1), causing cross-VLAN traffic leakage.

Adım Adım Çözüm

1
Analyze Spanning Tree Protocol (STP) Root Bridge Election
Switch-Alpha (priority 4096) has a lower priority than Switch-Gamma (16384) and Switch-Beta (32768).
STP elects the switch with the lowest numerical Bridge ID (Priority + MAC address) as the root bridge.
2
Analyze 802.1Q Native VLAN Tagging and Mismatch Symptoms
Frames from VLAN 10 sent untagged by Switch-Alpha are received by Switch-Beta and assigned to its native VLAN (VLAN 1).
802.1Q trunks do not tag frames originating from the configured native VLAN; mismatched native VLAN settings cause untagged frames to leak into the recipient switch's native VLAN.
3
Evaluate Inter-VLAN Communication and Layer 2 Forwarding Boundaries
Inter-VLAN communication between VLAN 10 and VLAN 20 requires Layer 3 routing, and 802.1Q tags remain at Layer 2.
VLANs divide physical switches into logical Layer 2 broadcast domains that strictly require Layer 3 routing for inter-VLAN forwarding.

Anahtar Kavram

Spanning Tree Root Election and 802.1Q Native VLAN Trunk Operations
Tahmini Süre:2m 0s
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Konular

Switching Concepts and VLANs

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