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Unmanaged switches and Nexus 2248TP Fabric Extenders

Stormphoenix
Beginner
Beginner

Hello,

I'm aware that if you plug a switch into a Nexus 2k fabric extender, the BPDU guard will disable the port when it detects STP traffic. What about if you plug in an unmanaged switch that doesn't support spanning tree? Im assuming the port wont block - is there anyone out there who has tried this, and does it work ok? (I know its not recommended Cisco design to do this, wondering what happens)

2 Replies 2

mullzkBern_2
Beginner
Beginner

The port won't block - as the dumb switch does not send any BPDU-Packets and BPDU-Guard just listens on those. Two caveats:

- If there is another switch behin the dumb switch and this switch participates in Spanning-Tree, the dumb switch forwards the BPDU and the guard disables the FEXes Port.

- Some unmanaged switches support spanning-tree and therefor send BPDUs as well!

Hi Jonathan

In general that may work but in addition to caveates described in previous post I'd like to add that usually problems occurs with specific configurations, traffic patterns etc...

If unmanaged switch will be simply forward the frames and won't participate in stp that doesn't guarantee normal work of the servers connected to it.

FEX ports used for end-host connections are caled HIF-ports - host- interface ports which means no switches, further extenders etc...

HTH,

Alex

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