MSTP with VSX guidelines

  • Path cost is not allowed to be configured on the ISL port.

  • VSX must be root for MSTP.

  • Layer 2 link connected parallel to ISL link is blocked by MSTP.

  • Do not configure port-specific spanning tree configurations on the ISL.

  • Multiple MSTP regions are not supported. Multiple instances are supported though (default + 64).

  • Topology changes for VSX LAGs are accounted on the active multichassis LAG role only.

  • MSTP is supported in both VSX and non-VSX environments.

  • The common bridge ID continues to be used even after the VSX split brain scenario is identified.

  • Interoperability with RSTP is not supported with a direct connection to the VSX environment. For example, interoperability between MST Instance 0 (CST) to RSTP is not supported. The VSX pair is configured as a nonroot switch.

  • STP configurations on VSX LAG ports must be the same on VSX switches.

  • Run the show running-config spanning tree and show running-config spanning tree vsx-peer commands for verifying that the following global parameters are the same on VSX switches:

    • STP mode.

    • STP region configuration for MSTP (config-name and config-revision)

    • STP instance to VLAN mapping

    • STP instance priority