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300-620 · Question #237

Refer to the exhibit. A Cisco ACI fabric is created with L2Out to N7K1 and N7K2 switches. The switches are running MSTP with native VLAN 10. The N7K1 and N7K2 act as the root bridge for VLAN 20. An EP

The correct answer is C. Encapsulate EPG Data with VLAN 10.. To receive MSTP BPDUs and enable proper spanning-tree interaction with external switches that utilize a native VLAN for MSTP, the Cisco ACI L2Out EPG must be encapsulated with that external native VLAN ID.

External Network Connectivity

Question

Refer to the exhibit. A Cisco ACI fabric is created with L2Out to N7K1 and N7K2 switches. The switches are running MSTP with native VLAN 10. The N7K1 and N7K2 act as the root bridge for VLAN 20. An EPG named Data has been created. The ACI fabric must be configured with these requirements:

  • The ACI fabric must receive MSTP BPDU.
  • The N7K1 switch must act as the root bridge for VLAN 20.

Which set of actions accomplishes these goals?

Exhibit

300-620 question #237 exhibit

Options

  • AEncapsulate EPG Data with VLAN 20.
  • BEncapsulate EPG Data with VLAN 10.
  • CEncapsulate EPG Data with VLAN 10.
  • DEncapsulate EPG Data with VLAN 20.

How the community answered

(38 responses)
  • A
    8% (3)
  • B
    5% (2)
  • C
    84% (32)
  • D
    3% (1)

Why each option

To receive MSTP BPDUs and enable proper spanning-tree interaction with external switches that utilize a native VLAN for MSTP, the Cisco ACI L2Out EPG must be encapsulated with that external native VLAN ID.

AEncapsulate EPG Data with VLAN 20.

Encapsulating the EPG Data with VLAN 20 is incorrect because MSTP BPDUs are transmitted on the native VLAN of the external MSTP domain, not on the specific VLAN where a switch might be the root.

BEncapsulate EPG Data with VLAN 10.
CEncapsulate EPG Data with VLAN 10.Correct

Encapsulating the EPG Data with VLAN 10, which is the native VLAN for the external MSTP domain, allows the ACI fabric to correctly receive and process MSTP BPDUs. This ensures proper spanning-tree operation between ACI and the external switches and allows ACI to respect the root bridge election for VLAN 20.

DEncapsulate EPG Data with VLAN 20.

Encapsulating the EPG Data with VLAN 20 is incorrect because MSTP BPDUs are transmitted on the native VLAN of the external MSTP domain, not on the specific VLAN where a switch might be the root.

Concept tested: Cisco ACI L2Out MSTP BPDU handling

Source: https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/5x/l2-configuration/cisco-aci-l2-configuration-guide-50x/m-l2-out.html

Topics

#L2Out#MSTP#BPDU#Root bridge#VLAN encapsulation

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