How the STP determinw that which Port should be Root Port, which port should b

Categories >> Certifications >> Cisco Certifications >> CCNA
Suggest New Category

How the STP determinw that which Port should be Root Port,
which port should be Designeted Port , Blocking Port and
Forwarding Port in Layer 2 STP topology........

Hi friends Thanks for posting the answer of above given
questions i agree with all of you that BPDU is the Protocol
that are used to determine this is clear to me..

But I want to Know the Process like Why it Blocked the port
Fa0/1 Insted of Fa0/2

waiting for Answer Posting ....
Thanks in Advance

Question Posted / vipin.lathawal

5 Answers
9057 Views
I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

How the STP determinw that which Port should be Root Port, which port should be Designeted Port , ..

Answer / jitu

hi
from your question i fell that you want to about process of
stp.
so
as we know that stp is the process in which we avoid the
switchnig loop.this loop is occured due to redudancy that
is alternate path.
this alternate path is given due to if one link get down
then another link get up and data flow remail continue.but
one draw back is there if both the link up then data found
two path and its create loop so to stop this we apply stp
i think you agree witj that ?

ok now the complete process i am going to expalin.

let take a example

switch1
| |
| |
| |
switch2 switch 3
| |
| |
switch4---------switch5
now supose that mac address of switch one is 1201
switch two is 8955
switch three is 1202
switch four is 2101
switch five is 9870

asume that all switch have default priorty value that is
32768
scine switch one has the higest mac addess then it wiil
become root bridge and rember that in root bridge all the
port are in forwarding mode.

Then follow up the connection the port is concetd to the
root bridge switch become root port and root port alway
become
f

follow the conection from switch one two all switch so port
directly conec in taht case port of switch 3 adn switch
four port become root port

no procced further
scine switch 4 and switch 5 port are closest port from
switch 3 and 4 and have the low cost then this port bill
become root port and alswys in forwarding mode

now bridge id come in acount to detrmine the deseignated
and non deseignated port
scine swich 4 have the lowest bid value then its port will
desigeinated and forwardin else switch five port will be in
blocking mode

Is This Answer Correct ?

5 Yes

4 No

How the STP determinw that which Port should be Root Port, which port should be Designeted Port , ..

Answer / jitendeta(abb india)

hi vipin
soory for the my typo mistake i have writen the switch one
have the highest mak address but it have lowest and you can
see it the mac table what i have writen.so i am again sorry
for my typo mistake.
now comes to your questions-
i am making the digarm for our Convinces
________
| |----------|-------|
| | ---------| |
----------- ----------
that is switch one is left one and switch 2 is right one
and it is conected through the cross cable?
now
acording to your network diagram we are using the redudant
link for the switch ok?
now if there is any redudent link is prsent there will be
loop ok ?
to avoid this loop we used stp?
now i assume that both the switch have default priorty that
is 32768 ok?
sorry i have some work so i will post rest of answer very
soon

Is This Answer Correct ?

1 Yes

0 No

How the STP determinw that which Port should be Root Port, which port should be Designeted Port , ..

Answer / jitendera sinha

wow if this explanatio is wrong then please let me know the
correct expalnation if you know
thanks in advance
if you are marking as know then please let other know on
what behalf you put it know

Is This Answer Correct ?

0 Yes

0 No

How the STP determinw that which Port should be Root Port, which port should be Designeted Port , ..

Answer / vipin.lathawal

Dear Jitendra,

I marked this answer No due to 2 reason....
The very first reason is that you stated that the Switch
with the highest MAC address will be selected as a Root
Bridge. This is Absolutely Wrong.
Becaue STP has the property that the switch with the Lowst
MAC address will be selected as The Root Bridge because all
switch has the Default ridge priority of 32768. So by
Default the Switch with low MAc address will be selected as
a Root Bridge.

2nd Reason to Mark Incorrect is that u r not posting what i
want to know.
Suppose that u have two switch , Switch-A and witch-B both
are connected with 2 cross cables by port fa0/1 and Fa0/2
on both switches. there is no third switch in this
topology. It does not matter which switch will be the root
Bridge but the FA0/1 will always be active on both switch
by default untill u set the bandwidth or link cost to
fa0/1. And the Port Fa0/2 will be in Blocking state on
either switch. why it is always blocking Fa0/2

why this is happening..... This is my question.

Is This Answer Correct ?

0 Yes

0 No

How the STP determinw that which Port should be Root Port, which port should be Designeted Port , ..

Answer / gtech

Sir ji...complete kariye..mai waiting list mei hu...ye
question pehle bhi kahi suna suna lagta hai...do it asap... :)

Is This Answer Correct ?

0 Yes

0 No

Post New Answer