What is the right answer to this question???

Unanswered Question
Jan 5th, 2010
User Badges:

Prior to 802.1w, Cisco implemented a number of proprietary enhancements to 802.1 D to improve convergence

in a Layer 2 network. Which of these statements is true?

A. Only Port Fast and UplinkFast are specified in 802.1w; BackboneFast must be manually configured.

B. Only UplinkFast and BackboneFast are specified in 802.1w; Port Fast must be manually configured.

C. Only Port Fast is specified in 802.1w; UplinkFast and BackboneFast must be manually configured.

D. None of the proprietary Cisco enhancements are specified in 802.1w.

E. Port Fast, Uplink Fast, and Backbone Fast are specified in 802.1w.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
johnnylingo Sun, 01/17/2010 - 21:36
User Badges:
  • Bronze, 100 points or more

Portfast, Uplinkfast, and Backbone fast are all included in 802.1w.  However, you must still manually set the portfast (edge) ports using the "spanning-tree portfast" command.

Ganesh Hariharan Mon, 01/18/2010 - 02:55
User Badges:
  • Purple, 4500 points or more
  • Community Spotlight Award,

    Member's Choice, February 2016


Genrally speaking cisco created Port Fast,Uplink fast and backbone fast to fix the holes and liabilities the IEEE802.1d standard presented.The drawbacks to these enhancements are only that her are cisco proprietary and need additional configuration.But the new 802.1w stadandard (RSTP) address all these issue in one right packages-just turn on RSTP and you're good to go.

Hope that clear your query!!



unixdayjob Fri, 01/22/2010 - 10:28
User Badges:

...depends on what the question means by "specified".  That's a rather obtuse use of the word ... maybe they meant, "included within".

Anyway, the answer is either D or E, depending on what they mean by "specified".  All the 'fast' features of backbonefast, etc., are included in 802.1w, but are from the IEEE and not Cisco.  Cisco did not make RSTP.  So, Cisco's proprietary enhancements to their STP to make it work mostly like RSTP are not technically included in RSTP.  The IEEE made (similar features in their own thing called) RSTP / 802.1w.  (Sometimes, when taking practice exams, you discover the hard way that you have to think in such 'detail').  From the document that burleyman posted:

Cisco enhanced the original 802.1D specification with features such as       Uplink       Fast,       Backbone       Fast, and Port Fast to speed up the convergence time of a bridged       network. The drawback is that these mechanisms are proprietary and need       additional configuration.

Rapid Spanning Tree Protocol (RSTP; IEEE 802.1w) can be seen as an       evolution of the 802.1D standard more than a revolution. The 802.1D terminology       remains primarily the same. Most parameters have been left unchanged so users       familiar with 802.1D can rapidly configure the new protocol comfortably. In       most cases, RSTP performs better than proprietary extensions of Cisco without       any additional configuration.

In other words, Cisco's enhancements to 802.1d are not the same/identical/equal to IEEE RSTP, but they function pretty much identically.

This makes me think "D".  But:


RSTP (IEEE 802.1w) natively includes most of the Cisco proprietary       enhancements to the 802.1D spanning tree, such as BackboneFast, UplinkFast, and       PortFast. RSTP can achieve much faster convergence in a properly configured       network, sometimes in the order of a few hundred milliseconds.

So, (me) judging by the way cert questions are sometimes worded, I'd go with E.  They probably  -mean-  E.  Discombobulating common english words to distract and confuse is a pretty cheap-shot way of testing someone's knowledge.  I think it's a question that needs improvement.

To make things more confusing, on my 2950 switches at home, and in the training videos I have, simply turning on rapid-pvst doesn't do it.  I still have to turn on portfast on each port.  I have the latest (free) IOS on my switches, too.  Just learn and do your best, passing is all that matters....


This Discussion