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New Member

Switch connectivity/Will be loop ?

Hi

we have two floors and three switchs.One switch(4500) is one floor and other two switch(3560) is other floor.Now two 3560 switch are connected with 4500 switch by two seperate cable.Now we want to connect another cable between  two 3560 swithch.Could you please tell me what i have to if i connect 3 cable between two 3560.Should i need any configuratin of all switchs.Is there any loop will be created if i connect 3 cable.Please have a look attachment for my drawing.It would be very much appreciated if you let me know your views.

Thanks

Aminul

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Switch connectivity/Will be loop ?

Hi

we have two floors and three switchs.One switch(4500) is one floor and other two switch(3560) is other floor.Now two 3560 switch are connected with 4500 switch by two seperate cable.Now we want to connect another cable between  two 3560 swithch.Could you please tell me what i have to if i connect 3 cable between two 3560.Should i need any configuratin of all switchs.Is there any loop will be created if i connect 3 cable.Please have a look attachment for my drawing.It would be very much appreciated if you let me know your views.

Thanks

Aminul

                    Attachments:

As told by other it wont cause a loop as PVST run by default in cisco switches it will automatically block the redundant path to avoid the loop,yes if you have manually disabled STP on switches then you can end in problem but genral practice no body used to disable stp on switches.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

4 REPLIES
Hall of Fame Super Silver

Re: Switch connectivity/Will be loop ?

Hello Aminul,

unless you have explicitly  disabled spanning-tree for one of the vlans of interest you should be fine and you don't need any specific command: the switches will decide which link to logically stop to avoid the loop.

you can check this using

show spanning-tree vlan vlan#

do it for each Vlan in all three switches to check. If all switches are running STP for all Vlans you are fine.

Ensure that C4500 is the root bridge for all vlans, this is done on C4500

Hope to help

Giuseppe

New Member

Re: Switch connectivity/Will be loop ?

Hi

Thanks everybody for precious comments. It would be helpful for me. I am going to do that.

Thanks

Aminul

New Member

Re: Switch connectivity/Will be loop ?

Aminul,

No , there will NOT  be a any loops, even if you connect your both 18th floor switches together via another cable as per you diagram. STP ( Spanning Tree Protocol) will find the redundant links and block one of your switch port/link as STP by default will only allow one forwarding port per segment unless  you configure STP load balancing. As soon as any of the active switch links goes down , STP port will move from Blocking port to Forwarding state thus bringing up the redundant link. If you down port come back up again then it will keep blacked by STP.

AS long as STP is running in you network (which by on by default i) , you will not have any problems by connecting another cable together.You can test this by unplugging the existing cable 1 on 4500 switch ( as per diagram),  traffic will  then be rer-routed via 3560 switch back to 4500. Run the continuous ping to  see how quickly STP will bring up the redundant link. You will hardly see any packet loss.

You need to configure the trunk link between 3560 switches.

All the best.

Salman

Re: Switch connectivity/Will be loop ?

Hi

we have two floors and three switchs.One switch(4500) is one floor and other two switch(3560) is other floor.Now two 3560 switch are connected with 4500 switch by two seperate cable.Now we want to connect another cable between  two 3560 swithch.Could you please tell me what i have to if i connect 3 cable between two 3560.Should i need any configuratin of all switchs.Is there any loop will be created if i connect 3 cable.Please have a look attachment for my drawing.It would be very much appreciated if you let me know your views.

Thanks

Aminul

                    Attachments:

As told by other it wont cause a loop as PVST run by default in cisco switches it will automatically block the redundant path to avoid the loop,yes if you have manually disabled STP on switches then you can end in problem but genral practice no body used to disable stp on switches.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

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