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Zorluk: OrtaInterswitch Connectivity and Trunking (802.1Q)

An administrator issues the `show interfaces trunk` command on Switch-A while troubleshooting inter-switch connectivity to Switch-B. The command output confirms that interface GigabitEthernet1/0/1 is actively trunking using 802.1Q encapsulation. However, syslog messages periodically display `%CDP-4-NATIVE_VLAN_MISMATCH` notifications because Switch-A is configured with native VLAN 30 while Switch-B uses native VLAN 1. Which two statements accurately describe how frames are handled across this link? (Select two.)

  1. Frames generated by hosts in VLAN 30 on Switch-A are transmitted across the trunk link without an 802.1Q header tag.Cevap
  2. Untagged frames arriving at Switch-B from Switch-A will be placed into VLAN 1, resulting in cross-VLAN traffic leakage.Cevap
  3. C
    Switch-A automatically forces interface GigabitEthernet1/0/1 into an err-disabled state upon detecting the VLAN mismatch.
  4. D
    Enabling Spanning Tree PortFast on GigabitEthernet1/0/1 suppresses the native VLAN mismatch logs while preserving trunk functionality.

Cevap

Frames originating from VLAN 30 on Switch-A are transmitted without an 802.1Q tag, and Switch-B associates incoming untagged frames with its own native VLAN (VLAN 1).
Under IEEE 802.1Q specifications, traffic matching the native VLAN of the transmitting switch interface is sent without an 802.1Q header. Because Switch-A has a native VLAN of 30, it sends VLAN 30 frames untagged. Upon receiving untagged frames, Switch-B associates them with its own native VLAN (VLAN 1). This results in unexpected cross-VLAN communication between VLAN 30 on Switch-A and VLAN 1 on Switch-B.

Adım Adım Çözüm

1
Identify the egress frame tagging behavior on Switch-A.
Because VLAN 30 is designated as the native VLAN on Switch-A, frames belonging to VLAN 30 are forwarded across the trunk without an 802.1Q tag.
Under 802.1Q trunking rules, frames matching the local native VLAN of the transmitting port are sent untagged.
2
Identify the ingress frame processing behavior on Switch-B.
Switch-B receives the untagged frame and assigns it to its configured native VLAN, which is VLAN 1.
Receiving switches process all incoming untagged Ethernet frames within whatever VLAN is locally configured as native on that receiving trunk port.

Anahtar Kavram

802.1Q Native VLAN Tagging Mechanics and Mismatch Behavior
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Konular

Interswitch Connectivity and Trunking (802.1Q)

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