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Zorluk: ZorVLAN Configuration and 802.1Q Trunking

A network administrator is inspecting an IEEE 802.1Q trunk link between two switches, `SW-CAMPUS-01` and `SW-CAMPUS-02`. The configuration of interface GigabitEthernet0/1 on `SW-CAMPUS-01` is:

text
interface GigabitEthernet0/1
switchport mode trunk
switchport trunk native vlan 50
switchport trunk allowed vlan 10,20,30,50

The configuration of interface GigabitEthernet0/1 on `SW-CAMPUS-02` is:

text
interface GigabitEthernet0/1
switchport mode trunk
switchport trunk native vlan 1
switchport trunk allowed vlan 10,20,30,50

A workstation connected to an access port on `SW-CAMPUS-01` in VLAN 50 transmits an unencapsulated Ethernet broadcast frame destined across the trunk link. Which of the following best describes how `SW-CAMPUS-02` will handle this frame upon arrival at its GigabitEthernet0/1 interface?

  1. It will accept the untagged frame and forward it to all active ports belonging to VLAN 1.Cevap
  2. B
    It will drop the frame immediately because VLAN 50 does not match the local native VLAN ID on the receiving switch port.
  3. C
    It will inspect the frame, dynamically inject an 802.1Q header with VLAN 50, and forward it to VLAN 50 ports.
  4. D
    It will route the frame to VLAN 50 ports directly because trunk ports automatically negotiate uniform native VLAN parameters per frame.

Cevap

The switch receiving the frame will accept the untagged frame and forward it to all active ports belonging to VLAN 1.
Under IEEE 802.1Q trunking, traffic belonging to the native VLAN configured on an egress trunk port is sent untagged. Because the sending switch has VLAN 50 set as native, VLAN 50 frames enter the link without an 802.1Q tag. Upon receiving an untagged frame on a trunk port, the receiving switch assigns it to its own configured native VLAN (VLAN 1). Consequently, the frame is forwarded within VLAN 1 on the receiving switch.

Adım Adım Çözüm

1
Analyze frame egress processing on the transmitting switch.
SW-CAMPUS-01 has native VLAN configured as VLAN 50. Therefore, frames belonging to VLAN 50 egress GigabitEthernet0/1 untagged (without an 802.1Q header).
By definition of IEEE 802.1Q standard, traffic belonging to the native VLAN of a trunk interface is transmitted untagged.
2
Analyze frame ingress processing on the receiving switch.
SW-CAMPUS-02 receives an untagged frame on GigabitEthernet0/1. Its configured native VLAN for that port is VLAN 1.
When a switch receives an untagged frame on an 802.1Q trunk port, it associates the frame with the local native VLAN configured on that specific receiving port.
3
Determine the forwarding behavior and operational impact.
The frame is processed as belonging to VLAN 1 on SW-CAMPUS-02, causing traffic to leak from VLAN 50 on the source switch into VLAN 1 on the destination switch.
Native VLAN mismatches do not block untagged frame forwarding by default; they result in cross-VLAN traffic leakage between different VLAN IDs.

Anahtar Kavram

802.1Q Native VLAN Operation and Mismatch Behavior
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Konular

VLAN Configuration and 802.1Q Trunking

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