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352-001 · Question #167

A switched network is being designed to support a manufacturing factory. Due to cost constraints, fiber-based connectivity is not an option. Which design allows for a stable network when there is a ri

The correct answer is A. Design the network to include UDLD to detect unidirectional links and take them out of service.. In a copper-only environment subject to manufacturing interference, UDLD detects unidirectional link conditions caused by physical layer disruptions and disables the affected port, preventing STP black holes.

Layer 2 Control Plane

Question

A switched network is being designed to support a manufacturing factory. Due to cost constraints, fiber-based connectivity is not an option. Which design allows for a stable network when there is a risk of interference from the manufacturing hardware in use on the factory floor?

Options

  • ADesign the network to include UDLD to detect unidirectional links and take them out of service.
  • BDesign the network to include EtherChannel bundles to prevent a single-link failure from taking down
  • CDesign the network to include loop guard to prevent a loop in the switched network when a link has
  • DDesign the network to include BackboneFast on all devices to accelerate failure convergence times.

How the community answered

(42 responses)
  • A
    74% (31)
  • B
    5% (2)
  • C
    14% (6)
  • D
    7% (3)

Why each option

In a copper-only environment subject to manufacturing interference, UDLD detects unidirectional link conditions caused by physical layer disruptions and disables the affected port, preventing STP black holes.

ADesign the network to include UDLD to detect unidirectional links and take them out of service.Correct

Manufacturing equipment emitting electromagnetic interference can degrade copper cabling such that only one direction of a full-duplex link functions, creating a unidirectional link that STP cannot detect on its own. UDLD sends periodic keepalive messages in both directions; if echoes stop arriving, it declares the link unidirectional and errdisables the port, preventing the switched network from forming forwarding loops or black holes caused by a link STP believes is bidirectional but is not.

BDesign the network to include EtherChannel bundles to prevent a single-link failure from taking down

EtherChannel bundles protect against a complete single-link failure but do not address unidirectional link conditions where one direction of a channel member still appears administratively up to STP.

CDesign the network to include loop guard to prevent a loop in the switched network when a link has

Loop guard prevents a designated port from transitioning to forwarding when BPDUs stop arriving, but it does not detect or remediate unidirectional links caused by physical interference.

DDesign the network to include BackboneFast on all devices to accelerate failure convergence times.

BackboneFast accelerates indirect-link failure convergence but does not address the root problem of interference-induced unidirectional links on the factory floor.

Concept tested: UDLD for unidirectional link detection in interference-prone environments

Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/udld.html

Topics

#UDLD#unidirectional links#switched network#interference

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