Sunday, 29 April 2012

CCNA – STP Questions


Question 1
Which three statements about RSTP are true? (choose three)
A. RSTP significantly reduces topology reconverging time after a link failure.
B. RSTP expends the STP port roles by adding the alternate and backup roles.
C. RSTP port states are blocking, discarding, learning, or forwarding.
D. RSTP also uses the STP proposal-agreement sequence.
E. RSTP use the same timer-based process as STP on point-to-point links.
F. RSTP provides a faster transition to the forwarding state on point-to-point links than STP does.

Answer: A B F
Question 2
Which two states are the port states when RSTP has converged? (choose two)
A. blocking
B. learning
C. disabled
D. forwarding
E. listening

Answer: A D
Explanation
RSTP only has 3 port states that are discarding, learning and forwarding. When RSTP has converged there are only 2 port states left: discarding and forwarding but the answers don’t mention about discarding state so blocking state (answer A) may be considered the best alternative answer.
Question 3
Which command enables RSTP on a switch?
A. spanning-tree mode rapid-pvst
B. spanning-tree uplinkfast
C. spanning-tree backbonefast
D. spanning-tree mode mst

Answer: A
Question 4
At which layer of the OSI model is RSTP used to prevent loops?
A. data link
B. network
C. physical
D. transport

Answer: A
Question 5
Refer to the exhibit. Given the output shown from this Cisco Catalyst 2950, what is the most likely reason that interface FastEthernet 0/10 is not the root port for VLAN 2?
Switch# show spanning-tree interface fastethernet0/10
STP_show_spanning_tree_interface.jpg
A. This switch has more than one interface connected to the root network segment in VLAN 2.
B. This switch is running RSTP while the elected designated switch is running 802.1d Spanning Tree.
C. This switch interface has a higher path cost to the root bridge than another in the topology.
D. This switch has a lower bridge ID for VLAN 2 than the elected designated switch.

Answer: C
Question 6
Which two of these statements regarding RSTP are correct? (Choose two)
A. RSTP cannot operate with PVST+.
B. RSTP defines new port roles.
C. RSTP defines no new port states.
D. RSTP is a proprietary implementation of IEEE 802.1D STP.
E. RSTP is compatible with the original IEEE 802.1D STP.

Answer: B E
Question 7
Refer to the exhibit. Each of these four switches has been configured with a hostname, as well as being configured to run RSTP. No other configuration changes have been made. Which three of these show the correct RSTP port roles for the indicated switches and interfaces? (Choose three)
RSPT_port_states.jpg
A. SwitchA, Fa0/2, designated
B. SwitchA, Fa0/1, root
C. SwitchB, Gi0/2, root
D. SwitchB, Gi0/1, designated
E. SwitchC, Fa0/2, root
F. SwitchD, Gi0/2, root

Answer: A B F
Explanation
The question says “no other configuration changes have been made” so we can understand these switches have the same bridge priority. Switch C has lowest MAC address so it will become root bridge and 2 of its ports (Fa0/1 & Fa0/2) will be designated ports -> E is incorrect.
Because SwitchC is the root bridge so the 2 ports nearest SwitchC on SwitchA (Fa0/1) and SwitchD (Gi0/2) will be root ports -> B and F are correct.
Now we come to the most difficult part of this question: SwitchB must have a root port so which port will it choose? To answer this question we need to know about STP cost and port cost.
In general, “cost” is calculated based on bandwidth of the link. The higher the bandwidth on a link, the lower the value of its cost. Below are the cost values you should memorize:
Link speedCost
10Mbps100
100Mbps19
1 Gbps4
SwitchB will choose the interface with lower cost to the root bridge as the root port so we must calculate the cost on interface Gi0/1 & Gi0/2 of SwitchB to the root bridge. This can be calculated from the “cost to the root bridge” of each switch because a switch always advertises its cost to the root bridge in its BPDU. The receiving switch will add its local port cost value to the cost in the BPDU.
One more thing to notice is that a root bridge always advertises the cost to the root bridge (itself) with an initial value of 0.
Now let’s have a look at the topology again
RSPT_port_states_explanation.jpg
SwitchC advertises its cost to the root bridge with a value of 0. Switch D adds 4 (the cost value of 1Gbps link) and advertises this value (4) to SwitchB. SwitchB adds another 4 and learns that it can reach SwitchC via Gi0/1 port with a total cost of 8. The same process happens for SwitchA and SwitchB learns that it can reach SwitchC via Gi0/2 with a total cost of 23 -> Switch B chooses Gi0/1 as its root port -> D is not correct.
Now our last task is to identify the port roles of the ports between SwitchA & SwitchB. It is rather easy as the MAC address of SwitchA is lower than that of SwitchB so Fa0/2 of SwitchA will be designated port while Gi0/2 of SwitchB will be alternative port -> A is correct but C is not correct.
Below summaries all the port roles of these switches:
RSPT_port_roles.jpg
+ DP: Designated Port (forwarding state)
+ RP: Root Port (forwarding state)
+ AP: Alternative Port (blocking state)
Question 8
Which two protocols are used by bridges and/or switches to prevent loops in a layer 2 network? (Choose two)
A. 802.1d
B. VTP
C. 802.1q
D. STP
E. SAP

Answer: A D
Question 9
Which switch would STP choose to become the root bridge in the selection process?
A. 32768: 11-22-33-44-55-66
B. 32768: 22-33-44-55-66-77
C. 32769: 11-22-33-44-55-65
D. 32769: 22-33-44-55-66-78

Answer: A
Question 10
Refer to the topology shown in the exhibit. Which ports will be STP designated ports if all the links are operating at the same bandwidth? (Choose three)
STP_designated_port.jpg
A. Switch A – Fa0/0
B. Switch A – Fa0/1
C. Switch B – Fa0/0
D. Switch B – Fa0/1
E. Switch C – Fa0/0
F. Switch C – Fa0/1

Answer: B C D
Explanation
First by comparing their MAC addresses we learn that switch B will be root bridge as it has lowest MAC. Therefore all of its ports are designated ports -> C & D are correct.
On the link between switch A & switch C there must have one designated port and one non-designated (blocked) port. We can figure out which port is designated port by comparing their MAC address again. A has lower MAC so Fa0/1 of switch A will be designated port while Fa0/1 of switch C will be blocked ->  B is correct.

23 comments:

Anonymous said...

Hello There. I discovered your blog the usage of msn.
This is an extremely neatly written article. I'll be sure to bookmark it and come back to learn extra of your helpful information. Thank you for the post. I will certainly return.
Here is my homepage ; Zulily coupon code

Anonymous said...

I love it when people get together and share opinions.
Great website, continue the good work!
Stop by my site - Turntable Cases

Anonymous said...

Hey there! Do you use Twitter? I'd like to follow you if that would be ok. I'm absolutely enjoying your blog and look forward to new updates.
Also visit my webpage ; Amp Racks

Anonymous said...

Malaysia & Singapore & brunei greatest on-line blogshop for wholesale & quantity korean add-ons, earrings, earstuds,
locket, rings, bracelet, bangle & hair accessories.
Offer 35 % wholesale rebate. Ship Worldwide
Feel free to surf my web page ... stitching wire jakarta

Anonymous said...

The other day, while I was at work, my cousin stole my iPad and tested to see if
it can survive a 25 foot drop, just so she can be a youtube sensation.

My apple ipad is now destroyed and she has 83 views.
I know this is completely off topic but I had to share it
with someone!
My web page : michigan unemployment office locations

Anonymous said...

Amazing! Its in fact remarkable piece of writing, I have
got much clear idea about from this post.
My web page - the truth teller show

Anonymous said...

Hi, after reading this remarkable paragraph i am too glad to
share my familiarity here with friends.
My web page :: Luis Souto ecommerce projects handled Westmarine

Anonymous said...

It's going to be finish of mine day, but before finish I am reading this enormous paragraph to improve my know-how.
My web page : Trick Photography and Special Effects

Anonymous said...

I have been surfing online more than 3 hours today, yet I never found any interesting article like yours.
It is pretty worth enough for me. In my view, if all web owners
and bloggers made good content as you did,
the web will be much more useful than ever before.
Review my page : mma fighters

Anonymous said...

I'm impressed, I must say. Rarely do I come across a blog that's equally educative and engaging, and let me tell you, you have hit the
nail on the head. The issue is something which too few people are
speaking intelligently about. I'm very happy I came across this in my search for something concerning this.
Visit my website neucopia review

Anonymous said...

I go to see each day some web sites and websites
to read articles, except this webpage presents quality based
writing.
My web blog : Family vacation at Upper James Manor

Anonymous said...

Very nice post. I just stumbled upon your blog and wished to
say that I have really enjoyed surfing around your weblog posts.
After all I will be subscribing to your rss feed and I am hoping you write again
very soon!
Have a look at my blog post :: Gambling

Anonymous said...

What's up, I would like to subscribe for this weblog to get hottest updates, thus where can i do it please help.

Feel free to visit my homepage :: time to stop smoking tobacco

Anonymous said...

Do you mind if I quote a few of your posts
as long as I provide credit and sources back to your site?
My blog site is in the very same area of interest as yours and my visitors would truly benefit from a
lot of the information you present here. Please let me know
if this alright with you. Regards!

Here is my web blog domains for sale

Anonymous said...

What a information of un-ambiguity and preserveness of valuable familiarity regarding unpredicted emotions.


my site ... facebook quotes

Anonymous said...

Unquestionably believe that which you said. Your favorite reason seemed to be
on the internet the easiest thing to be aware of. I say to you, I definitely get irked while people think about worries that they plainly don't know about. You managed to hit the nail upon the top as well as defined out the whole thing without having side effect , people can take a signal. Will likely be back to get more. Thanks

Take a look at my site ... Botox Services Manchester

Anonymous said...

My brother suggested I might like this website. He was totally right.
This post truly made my day. You can not imagine just how much time I had spent for this info!
Thanks!

my blog post - Consultant Appointments Manchester

Anonymous said...

Excellent post. I was checking continuously this blog and I am impressed!
Extremely useful information specially the last part :) I care for such information a lot.
I was seeking this particular info for a very long time.
Thank you and good luck.

my blog - los angeles dj

Anonymous said...

I read this article fully concerning the difference of
newest and earlier technologies, it's remarkable article.

My weblog http://www.cuteteenporn.net/

Anonymous said...

Sweet blog! I found it while searching on Yahoo News.
Do you have any tips on how to get listed in Yahoo News?
I've been trying for a while but I never seem to get there! Appreciate it

my web site: naked teen

Anonymous said...

Nice post. I was checking continuously this blog and I am impressed!
Very useful information specifically the last part
:) I care for such information much. I was looking for this
particular info for a long time. Thank you and best of luck.


My page - www.anal4firsttime.org

Anonymous said...

It is appropriate time to make some plans for the longer term and it's time to be happy. I have learn this publish and if I may I desire to suggest you some attention-grabbing things or tips. Perhaps you could write next articles regarding this article. I wish to read even more things about it!

Take a look at my web-site ... get free sex xvideo clip (dansksextube.dk)

Priya Nain said...

Keep up the good work. your blog is one of the most helpful, neat and clearly written i have seen tillnow in ccna . you deserve accolades