![cst to mst cst to mst](https://www.ccexpert.us/global-configuration/images/7876_275_75.jpg)
While not the optimal solution, it ensures that no changes go unnoticed and no black holes occur in a single VLAN due to the topology changes. It’s hard to automatically map VLAN-bounded STP’s to the MSTI’s and so the simplest way to accomplish the desired behavior is to join ALL PVST+ trees with the CST.īy connecting PVST+ trees to the CST, the solution ensure that changes in any of PVST+ STP instances will affect the CST and all MSTIs as a consequence. The interoperation model needs to ensure that internal MSTI’s could be aware of changes in any of PVST+ trees. MSTP runs multiple MSTIs inside a region and maps them all to CIST on the border ports. SW1(config-if) spanning-tree mst simulate pvst disable SW1(config)# interface GigabitEthernet0/22 You have the option to disable interoperation with connected RPVST+ ports and this can be performed on a global or per port basis. That is, by default, all interfaces on the switch interoperate between MST and Rapid PVST+. The PVST simulation feature enables this seamless interoperability. MST interoperates with Rapid PVST+ with no need for user configuration.
![cst to mst cst to mst](https://www.timejones.com/Chicago.jpg)
A boundary port connects to a LAN, the designated switch of which is either a single spanning tree switch or a switch with a different MST configuration. MST switches can send either Version 0 configuration and topology change notification (TCN) BPDUs or Version 3 MST BPDUs on a boundary port. To restart the protocol migration process (force the renegotiation with neighboring switches), enter the clear spanning-tree detected-protocols command.Īll Rapid PVST+ switches (and all 8021.D STP switches) on the link can process MST BPDUs as if they are 802.1w BPDUs. A switch might also continue to assign a boundary role to a port when the switch to which this switch is connected has joined the region. However, the switch does not automatically revert to the MST mode if it no longer receives 802.1D BPDUs because it cannot detect whether the 802.1D switch has been removed from the link unless the 802.1D switch is the designated switch. In addition, an MST switch can detect that a port is at the boundary of a region when it receives an 802.1D BPDU, an MST BPDU (Version 3) associated with a different region, or an 802.1w BPDU (Version 2). If this switch receives an 802.1D configuration BPDU (a BPDU with the protocol version set to 0), it sends only 802.1D BPDUs on that port. Interoperability with 802.1DĪ switch that runs MST supports a built-in protocol migration feature that enables it to interoperate with 802.1D STP switches. All BPDUs will come from the IST root, not from the individual MSTI Root Bridges. It does not see the individual mappings of VLANs to instances. When a switch running PVST+ is connected to a switch running MST and part of a MST region, the PVST+ Switch only sees the BPDUs of the IST.