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New Member

Will I need Spanning Tree - when I have only one Switch


Could you let know if I would need to enable Spanning Tree - when I have only one switch in the network - this switch connects on North bound to Routers on South Bound to multiple servers via FEX/2k

Network Something Like this

                            Router A   


                              | LAG



                              |     \     \ ( Atleast 2 Links each) - FEX - Fabric Links

                              |     \      \

                              |     \      \

                             2K    2K    2K

                              |     \     \ ( Atleast 4 Links to each server from 2K to Server ) Servers connect to only one FEX

                              |     \      \

                              |     \      \

                         ServerA   B    C

Is there a possibilty of loops in this scenario



New Member

Will I need Spanning Tree - when I have only one Switch

One scenario is a accidental self loop on the 5K - yet that is due to a misconfiguration /bad patching.

Are there any other scenarios which could cause a loop ! which needs loop prevention to be considered



VIP Purple

Re: Will I need Spanning Tree - when I have only one Switch

This answer is valid if u have only one swicth:

The purpose of spanning tree protocol is to allow redundant connections between switches to exist without creating loops that would bring the network down.

If You need more than one switch to create a loop and resolve via STP.

With a single switch, STP is moot



Dont forget to rate helpful posts.

Super Bronze

Re: Will I need Spanning Tree - when I have only one Switch


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As you noted, it's good practice to still enable STP, even on one switch, incase a loop is accidentally created, just as looping two of the switch's ports.

FEXs shouldn't be, by themselves, creating L2 loops.

However, you example of multiple links to a server, would allow the server to loop those ports.  If the server is correctly configured, this shouldn't happen, but again, STP should be enabled to avoid accidental loops.