How STP influence the Traffic

jskfan
jskfan used Ask the Experts™
on
How STP influence the Traffic

on the diagram below, PC2 is connected to  Switch SW3 that has a blocked port on the link to SW1. Now Traffic from PC2 to PC1 will it go from SW3 to SW2 then to SW1 or it stiil can go straight from SW3 to SW1 then to PC1

Thank you
stp
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Jeremy WeisingerSenior Network Consultant / Engineer
Commented:
It will need to go through switch 2.
Instructor
Top Expert 2015
Commented:
No.  The traffic will go from PC2-SW3-SW2-SW1-PC1.

If you make SW1 the root, that will fix it (assuming the links are the same speed).
SouljaSr.Net.Eng
Top Expert 2011
Commented:
I  believe both previous responses are actually in agreement.  The main information missing is which switch is root. base on the diagram Switch 2 must be root as all downstream designated ports are not blocked, so the two previous comments are correct.
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Author

Commented:
I agree..I just wanted to make sure the blocked port does not transport traffic from hosts.

is there a way to confirm that when pinging  from PC2 to PC1 it will not take the direction of the blocked port ?

Author

Commented:
I mean other than wireshark that might show the directions taken by ICMP (PING),  is the debug able to show that?
Don JohnstonInstructor
Top Expert 2015

Commented:
Not from the PC's.  You can look at the MAC address tables or the spanning tree topology on the switches.
SouljaSr.Net.Eng
Top Expert 2011

Commented:
If you go on the switches and do

sh spanning-tree vlan x

It will show you which ports is forwarding and which are blocked for that vlan.

Author

Commented:
Thank you

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