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352-001 · Question #531

Refer to the exhibit. You are designing a data center migration from one location to another, which requires all existing VLANs spanned to the new data center to maintain host IP addressing. Two tempo

The correct answer is A. Perform BPDU filtering over the trunk links. BPDU filtering on the inter-DC trunk links blocks Spanning Tree BPDUs from crossing between locations, ensuring that a Layer 2 topology event in one data center cannot propagate to and destabilize the other.

Layer 2 Control Plane

Question

Refer to the exhibit. You are designing a data center migration from one location to another, which requires all existing VLANs spanned to the new data center to maintain host IP addressing. Two temporary Gigabit Ethernet circuits are available to extend the VLANs at Layer 2 to the new location as trunk links between core switches in each location. Which solution provides maximum fault isolation between the two data centers to ensure that a Layer 2 issue in one data center does not affect the other during the migration?

Exhibit

352-001 question #531 exhibit

Options

  • APerform BPDU filtering over the trunk links
  • BEnable STP PortFast on host ports within each data center
  • CRun the dual links as multichassis Etherchannel trunk between core switches within each location
  • DPerform HSRP filtering over the trunk links to maintain active HSRP gateways within each data

How the community answered

(34 responses)
  • A
    59% (20)
  • B
    24% (8)
  • C
    6% (2)
  • D
    12% (4)

Why each option

BPDU filtering on the inter-DC trunk links blocks Spanning Tree BPDUs from crossing between locations, ensuring that a Layer 2 topology event in one data center cannot propagate to and destabilize the other.

APerform BPDU filtering over the trunk linksCorrect

BPDU filtering prevents Bridge Protocol Data Units from being sent or received on the trunk interfaces connecting the two data centers. Without BPDUs crossing the link, the STP domains in each DC remain completely independent. A topology change, TCN flood, or root bridge election storm in one DC is fully contained and cannot trigger reconvergence in the other DC.

BEnable STP PortFast on host ports within each data center

PortFast on host ports only bypasses the listening and learning states for end-device ports within a single DC and has no effect on STP propagation across the inter-DC trunk links.

CRun the dual links as multichassis Etherchannel trunk between core switches within each location

Multichassis EtherChannel provides link redundancy and increased bandwidth between core switches but does not isolate or limit STP domain boundaries between the two data centers.

DPerform HSRP filtering over the trunk links to maintain active HSRP gateways within each data

HSRP is a first-hop gateway redundancy protocol; filtering HSRP messages has no effect on Layer 2 Spanning Tree propagation between data centers.

Concept tested: BPDU filtering for Layer 2 domain isolation

Source: https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10556-16.html

Topics

#BPDU filtering#fault isolation#VLAN extension#data center migration

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