C9500 StackWise Virtual & Spanning-Tree

[mrshabbs]

Hi All, we are deploying a pair of C9500's configured as a stackwise virtual pair. Connected to these switches are multiple 4 switch 9300 access layer stacks with dual-homed multi ethernet-channels back to the 9500's. The uplink connections are typically patched as follows:

9300-access-sw1 TeG1/1/1 - 9500-core-sw1 Te1/0/1 (interface configured as member of Port-Channel100)

9300-access-sw-1 TeG4/1/1 - 9500-core-sw1 Te2/0/1 (interface configured as member of Port-Channel100)

The above configuration is in simplest form, i.e. more access stacks will be added and connected to the core in the same way as the above example. The core will host the SVI's for the 10 or so vlans in use.

My question is does this network require any form of spanning tree (i.e. rpvst), or is this considered a layer 2 loop free because of the stackwise virtual technology deployed at the core?

Thanks All!!

[marce1000 · Accepted solution]

 - Ref : https://community.cisco.com/kxiwq67737/attachments/kxiwq67737/6016-discussions-lan-switching-routing/468722/1/q-and-a-c67-738577.pdf
                Q   What is the maximum number of supported STP
                      instances?
               A StackWise Virtual can support up to 128 STP instances using
                   the R-PSVT protocol. For increased scale, IEEE 802.1s Multiple
                  Spanning Tree (MST) is the recommended protocol.

         (you still need spanning tree)

 M.

[mrshabbs]

Hi - please elaborate why spanning-tree is required? I assumed as all cross-switch links are port-channels presented as single logical links hence this elimates stp considerations?

[marce1000]

           - It's safer if someone creates a loop accidently ; it also leads to consistent ability for bpduguard settings on client switches if desired

 M.

[Joseph W. Doherty]

It's L2 loop free.

However, a STP variant is still recommended in case of accidental L2 loop creation.  I would recommend one of the rapid variants.  Further, to minimize STP processing per VLAN, you could use MST.

[Richard Pidcock]

Agree with comments above, good idea to run STP to protect against accidental loop creation, and would definitely run a rapid variant of STP.