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Cisco Bug: CSCvs84502 - [] MSTP: Ports moving to DSGN/BLK state

Last Modified

Oct 04, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases


Description (partial)

On reloading a MSTP root node with multiple connections to peer routers, the MSTP topology is unstable for 30s before converging. Very high numbers of MAC flushes are requested (see "show spanning-tree mst [instance] topology flushes"). In high scale situations, the port states may get stuck due to the large number of MAC flushes requested.

Router boot with MSTP configured with a non-zero bring-up delay timer.

Note: not all platforms are impacted. This is known to affect NCS5500, but it is likely to impact other similar platforms such as NCS540/NCS560.

Higher scale (more interfaces and/or VLANs) will see more network churn and more MAC flushes.
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