400-007 Question #160: Real Exam Question with Answer & Explanation

The correct answer is C: The max_age and forward delay parameters can be adjusted to speed up STP convergence. In IEEE 802.1d STP, the max_age and forward_delay timers are the adjustable parameters that directly control failure detection speed and port state transition time, allowing faster convergence after a link or node failure.

Question

Refer to the exhibit. This network is running legacy STP 802.1d. Assuming "hello_timer" is fixed to 2 seconds, which parameters can be modified to speed up convergence times after single link/node failure?

Exhibit

Options

AThe transit_delay=5 and dpdu_delay=20 are recommended values, considering helto_timer=2
BOnly the maximum_transmission_halt_delay and diameter parameters are configurable
CThe max_age and forward delay parameters can be adjusted to speed up STP convergence
DOnly the transit_delay and bpdu_delay timers are configurable parameters in 802.1d to speed up

Explanation

In IEEE 802.1d STP, the max_age and forward_delay timers are the adjustable parameters that directly control failure detection speed and port state transition time, allowing faster convergence after a link or node failure.

Common mistakes.

A. transit_delay and dpdu_delay (bpdu_delay) are not recognized 802.1d STP timer parameters, and the values cited do not map to any valid STP convergence configuration.
B. maximum_transmission_halt_delay is not a standard 802.1d STP parameter; network diameter is a design input used to calculate recommended timer values rather than a directly configurable convergence timer.
D. transit_delay and bpdu_delay are not standard IEEE 802.1d STP configurable timer names; the correct convergence timers are max_age and forward_delay.

Concept tested. IEEE 802.1d STP convergence timer tuning

Reference. https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/19120-122.html

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