Connectivity loss in hybrid Fabric/MSTP loop during link failover (VOSS & Cisco)

Dragonfly — Tue, 12 May 2026 08:50:22 GMT

Hello,

I am currently migrating a Cisco environment to Extreme VOSS (Fabric Engine/Fabric Connect).

Topology Setup: The physical loop is as follows: Cisco-01 <--> Cisco-02 <--> Extreme-02 <--> Cisco-03 <--> Extreme-01 <--> Cisco-01

Cisco Side: 3x switches
Extreme Side: 2x VOSS switches

The Issue: Connectivity is stable in the normal state. However, Cisco ports initially showed Bound(RSTP) when connected to VOSS on certain interfaces. To resolve this, I used the command "no spanning-tree mstp force-port-state enable" on the Extreme interfaces connected to the Cisco switches. This successfully forced the ports to p2p mode, and everything works fine when the loop is fully connected.

The Redundancy Problem: When I unplug a link to test redundancy, connectivity drops and does not recover, even though a valid redundant path exists.

Observations:

Port Status: Cisco ports correctly show p2p when connected to VOSS.
Root Bridge Conflict: Cisco-03 appears to be isolated; it claims to be the Root Bridge, while all other switches see Cisco-01 as the Root.
BPDU Statistics: On VOSS, show spanning-tree mstp port statistics reveals highly asymmetric Rx/Tx BPDU counts (e.g., very high Rx but near-zero Tx on some ports).
Configuration Constraint: VOSS is NOT the Root Bridge (Cisco-01 is the designated Root). My management currently refuses to change the Bridge Priority on the Extreme switches.

Re: Connectivity loss in hybrid Fabric/MSTP loop during link failover (VOSS & Cisco)

WillyHe — Tue, 12 May 2026 21:21:33 GMT

Maybe this link can help

https://extreme-networks.my.site.com/ExtrArticleDetail?an=000082836&q=how%20to%20connect%20SPBM-FC%20to%20MSTP

regards

WillyHe

topic Connectivity loss in hybrid Fabric/MSTP loop during link failover (VOSS & Cisco) in ExtremeSwitching (VSP/Fabric Engine)

Connectivity loss in hybrid Fabric/MSTP loop during link failover (VOSS & Cisco)

Re: Connectivity loss in hybrid Fabric/MSTP loop during link failover (VOSS & Cisco)