Because the cost to follow the link out G0/1 = 4 (plus the botton link, cost of 19) = 23
As opposed to the top link with is 19 + the left link with is also 19 = 38

Since 23 < 38, the G0/1 port wins.

The top link is a cost of 19.
The right link IS a cost of 4.
The left link is a cost of 19.
And the bottom link is a cost of 19.

kenkhan35@gmail.com

Is there a requirement for the new ccna 200-120 before attempting to take it? Thank for sharing.

So SwiB root cost= 19+4=23 and SwiA= 19(better)

So the Designated port is not elected by the lowest MAC.

For Q9:

Cisco by default STP has a priority value of 38768 but being on the vlan1 this value increases to 32769 ….

For Q9:

Bridge priority must be an increment of 4096.. It can be 0 4096 8192 … 32768 …
32769 is not valid..

Reference ccna discovery 3 chapter 3..

Am I being wrong??

q9: we see the lowest priority and in the q9 is 32768 and then we see the lowest mac address.

in this case BID = default bridge priority value 32768+Vlan iD (minimum 1 /(1-4096) ) + Mac address.
if so 32768 can not be the answer. (ccna 3 exploration 5.2.3) — show spanning-tree command will add the vlan id to show the priority value of the root id. Please help. Many thanks – Mei

if it was C, than C answer is true if and only if the “other interface” that has a lower path cost to the root is assigned to the same VLAN2.
Which exactly means that A is the answer (more interfaces to root in VLAN2).

As C is not referring to VLANS (and the switch is running a per vlan stp right?) it cannot be true, at least it is not the best choice.

The question asks which is the “most likely reason”, not the REAL TRUTH.
So for me the most likely is that another port in VLAN2 has a path to root switch.

Switch A connects to Switch C through Gi port (port on switch A towards Switch C is still Fa)
Switch B connects to Switch A through Gi0/1 on Switch B
Switch B connects to Switch D through Gi0/2 on Switch B
Both ports in between Switch C and Switch D is Gi ports .

Will the Low speed connection to Switch A be RootPort and Gi0/2 which connects to Switch D in AP??

<— cost to root is 8

SWITCH A Fa0/1 Gi0/1 SWITCH B
MAC ADDRESS ——————— MAC ADDRESS
0013.8039.9500 0013.80d7.d580 |
| | | cost to root is 8
| Gi0/1 | Gi0/2 | but port is lower
| | V than Gi/1
| |
| |
| |
| Fa0/1 | Gi0/1
| |
SWITCH C Gi0/2 Gi0/2 SWITCH D
MAC ADDRESS ———————- Mac Address
0013.8030.5e80 0013.80c7.9700
Root bridge

Will the low speed path preferred against Gi path ?

Q2: there is no blocking , but discarding is available

Sorry for my bad english. Just from Russia.

I think the Gigabit interface should negotiate with the bandwidth of fast ethernet. How can a fast ethernet interface have a speed of 1Gbps?

the questions asks, “the most likely reason not to be the root port”

A -> there is another port
(just the presence of another port in the same vlan doesn’t make this port ALT BLK)

C -> the cost is higher (this does)

hope this helped somebody

@gobregon: exactly! when a GIG and a FastEthernet port are connected the maximum transmission speed is 100Mbps… because the GIG link negotiates the speed and also “becomes” a FaE port the link cost is 19 NOT 4 !!!

nevertheless, the solution is rigtht, just the explanatation is a little bit bugged ;)

PVST+ option do not supports RSTP for that,
RSTP cannot operate with PVST+ is correct too

Answer: A B E

cost to root lower than SwitchB” but they say “MAC address of SwitchA is lower than that of

SwitchB” that it means cost to root between SwitchA & SwitchB are equal ????

(Sorry my English is not strong)

On the first part of the explanation said:

“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.”

On the final of the sentence said the letter E is correct. so this really correct?
Because on SW C F0/2 port is a DP (designated port) I´m right???

Have good wind´s from Brazil =)

Reason being is that although the default cost of a gig link is indeed 4, the operating cost of SwitchB gi0/2 in real life will actually be 19 because the links on the segment will autonegotiate to fastethernet 100 megabit speed since one side is a gig link and the other side is only a fastethernet.

I verified this by setting up the scenario in Packet Tracer and indeed SwitchB gi0/2 autonegiated down to 100 megabit. Hope this clarifies things further to you all =)

Q7, explanation regarding DP selection is incomplete.

Based on Wendell Odom CCNA ICND2 book (Cisco official guide), page 70, “the DP on each LAN segment is the switch port that advertises the lowest cost HELLO on to the LAN segment. In effect, the switch with the lower cost to reach to the root, among all switches connected to a segment, becomes the DP on that segment. If the advertised cost tied, the switches break the tie by choosing the switch with the lower bridge ID.”

Based on this explanation, on the segment between Switch A and Switch B, Switch A advertises 19 to reach root, whereas Switch B advertises 23 to reach root. Therefore Switch A Fa0/2 becomes DP.

-Discarding:This state is seen in both a stable active topology and during topology synchronization and changes.
-Learning:This state is seen in both a stable active topology and during topology synchronization and changes.
-Forwarding:This state is seen only in stable active topologies.

So There’s no blocking state in RSTP,, and the learning state can be seen in a stable network

what is root network segment? <= I think this is the reason A is wrong!

the image must be wrong, because the column Prio.Nbr should be:

128.10
128.10
128.10

and not as it is now.

I think the dump by shikhar is enough to take preparation of ccna.

I still don’t get Question 5

A. This switch has more than one interface connected to the root network segment in VLAN 2

that must be true, although it may or may not considered to be an answer.

C. This switch interface has a higher path cost to the root bridge than another in the topology.

How can we know that? maybe other switch has a interface with a higher path than this one and is also blocking it’s port, for a given topology, more than one ports may be in blocking state.

If the answer would be “… than another in the switch” that would be right, but for the given “topology”, other switches may be blocking some ports.

Also, if you see the other vlans, the cost is the same (19 = 100 Mb/s ), so why will we assume that this port has a higher path?

Thanks.

Q#8

Q:7

a typo mistake but the point is at last which switch is going to block its one port is Switch A’s Fa0/2.

I understand well enough ;) what I mean, is that in point 4 you write that the cost from SW B through SW C to SW C is 23, whereas in point 5 you write that this cost is 8, so please make up your mind and decide, whether it is 8 or 23?!

and no hard feelings of course :)

Lowest Cost is defiantly 8:
Plz Consult the links below for better understanding:

http://www.ciscopress.com/articles/article.asp?p=426642&seqNum=3
and a video about STP
http://www.youtube.com/watch?v=y-SppCHx1Qs

4) Now SWITCH B CAN REACH Root Bridge via both switches but it will choose for the lowest cost ie is via SWITCH D (TOTAL COST 4(SWITCH B TO SWITCH D) + (SWITCH D TO SWITCH C)19= 23)

5) but according to the rule number 2 SWITCH B has a root path cost of 4+4=8

So what is exactly the root cost from switch B to switch C? 23 or 8? :)

Try it in packet tracer and you will then come to conclusion and also please visit the links which i have mentioned in my previous post.

Thanx 9tut for the great site and help i have successfully passed CCNA today with 881/1000 .
next is for CCNP. Best of luck for others who are going to take the exam.