STP Questions
Here you will find answers to STP Questions
If you are not sure about STP, please read my Spanning Tree Protocol tutorial first.
Question 1
Which switch will be chosen as root bridge and why?
A. Sw-B, because it has the highest MAC address
B. Sw-A, because it has the lowest MAC address
C. Sw-C, because it has the lowest priority
D. Sw-D, because it has the highest priority
Answer: C
Explanation
The bridge with the lowest bridge ID will become the root bridge. The bridge ID = Priority + MAC so the lowest priority will be chosen first. If all switches’ priorities all equal then their MAC will be compared (the lowest is the best).
Question 2
Spanning Tree Protocol has created a loop-free logical topology in the network that is pictured. How many ports have been placed in the blocking mode?
A. two
B. none
C. three
D. one
E. four
Answer: A
Explanation
The best way to solve this question is to suppose that one of these switches is the root switch (bridge). For example, if we choose S2 the root bridge and all of its ports will be in forwarding state (so that they are not blocked).
Also suppose that S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked.
The most difficult problem is that how can we know which port on S4 will be in blocking state. Well, it depends on the Sending Port ID on S4 (Port ID = port priority + port index). If using default values, the default port priority’s value is the same, so S4 will compare port index values, which are unique to each port on the switch. One more time, we suppose S4 connects to S1 via Fa0/1 and S4 connects to S3 via Fa0/2. Because Fa0/2 is inferior to Fa0/1, S4 will select the port connected with Fa0/1 as its root port and block the other port.
Question 3
What is the way that Spanning Tree Protocol prevents switching loops based on the exhibit provided?
A. STP shuts down S3 to eliminate the switching loops.
B. STP identifies cables that must be disconnected to eliminate the redundant paths.
C. STP load balances traffic evenly across the redundant links.
D. STP places ports into the blocking state to disable the redundant paths.
E. STP allows the switches to communicate with a router that makes the traffic forwarding decisions.
Answer: D
Question 4
The following network was designed to provide reliability through redundancy.
Both of the IDF switches, S3 and S4, are in connection with both of the MDF switches, S1 and S2. A loop-free switching environment is nedded, which configuration scenario will achieve this?
A. Spanning Tree Protocol should be running on all switches.
B. Spanning Tree Protocol should be running only on the root bridge.
C. Spanning Tree Protocol is not needed in this network.
D. Spanning Tree Protocol should be running on only the MDF switches S1 and S2.
Answer: A
Question 5
Which two values are used by Spanning Tree Protocol to elect a root bridge? (Choose two)
A. Amount of RAM
B. Bridge priority
C. IOS version
D. IP address
E. MAC address
F. Speed of the links
Answer: B E
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 802.1 D STP.
E. RSTP is compatible with the original IEEE 802.1 D STP.
Answer: B E
Question 7
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
“Also suppose that S1 has higher priority than S3 -> the port on S3 connected to S1 will be blocked.”
So on switches that connect multiple segments, the switch with the +higher+ priority wins?
i thought it was LOWER priority wins…
http://www.ccnacertificationguide.com/Root_Bridge_Election.php
If the cost is the same on a given segment, the port with the lowest bid becomes the designated port. The other port on this segment will be put into the blocking state.
Question 7 is C not A lowest MAC wins
Yes I am an idiot… I see the “8″ now.
That is correct, the answer to Question 7 is A because it has the lower priority (32768) – Please read about the election process again.
I think on question 2 you got it backwards, If the switch has a lower priority, then its ports will be in fowarding / root port mode and the inferior higher priority switch will be in blocking mode???
The reason the lower Priority and MAC ID’s win the root election, is to help retain compatibility with older equipment. Older Switches may not support features of newer switches; therefore, some aspects like RSTP on newer switches would disable the network on the older LAN. You would however, lose the ability of RSTP on the newer switches.
I would have thought answer D to question 4 is just as valid as answer A. See: http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613.shtml
“Note: Switches that do not run STP still forward the bridge protocol data units (BPDUs) that they receive. In this way, the other switches on the VLAN that have a running STP instance can break loops. Therefore, STP must run on enough switches in order to break all the loops in the network. For example, at least one switch on each loop in the VLAN must run STP. You do not need to run STP on all switches in the VLAN. However, if you run STP only on a minimal set of switches, a change to the network can introduce a loop into the network and can result in a broadcast storm.”
If we run STP on just two switches that would be enough to put one port into blocking mode thus breaking the loop??
anyone have any dumps on the fram-relay sim where you map layer to ip address
and also ask about what password you use to access dubi router
four part sim question?
Lost of guys are confused the blocking state of a switch
@PHxAZ it’s:
http://www.9tut.com/ccna-hotspot-questions
On question 2 under the second answer diagram, the Switch 4, Fa0/1 isn’t a root port, is it? Shouldn’t it be a designated port? Or am I wrong.
Disregard previous.
Q1 question: How come that we have “Priority 1″ and “65535″ in the exhibit in question??
Those values are NOT vlaid values for spanning-tree priority?? The correct values starts from 0 and steps in increments of 4096?? so did I miss anything ?
Can you send me the latest updates, Thank you
@Bruno
Hi! yes – you are missing the Extended System ID, and CISCO per-VLAN STP approach.
As every switch has its VLAN 1 in place this will make its priority 0 + 1 = 1.
In case of 65535 the Extended is disabled making possible to span for the entire pool of 0 – 65535. Some switches wont allow the Extended SysID to be disabled but I think on catalyst 6500 for example, putting a priority on 65535 will make that switch not to be candidate for ROOT Bridge ever.
Regards
Q6 shouldn’t “A” be correct too? RSTP should only be able to support PVRST and MIST right?
@vin
According to Wendell Odem-ICND2, P.88, it says PVST+ does not support RSTP. But a quick google search says they can work together. Is Wendell wrong on this, anyone know?
@Anonymous,
I started hating Wendell Odom when I read the first few chapters of his ICND1/2 books… he is impossible to understand. Read the Todd Lemle book Edition 6th
@Anonymous
yep, try to read for Todd Lammle or Richard Deal.
is this updated?
2 questions can be found in the TestKing software for 640-816.
Passed ICND2 today with 944!! I didn’t have any of these questions on my exam
could you tell me how many questions are from P4S with 204 questions?
@Barry
I find the opposite – I prefer Odams books to Lammles. Quite easy to understand.