A frequent CCIE-level written exam topic is STP (PVST+) to RSTP (Rapid-PVST) migrations. This post covers the high points you should be aware of.
Some Quick Notes
- BackboneFast and UplinkFast are no longer necessary in RSTP environments as the equivalent advantages are built-in to RSTP
- BPDUs are version 2 in RSTP which is compatible with version 0
- All ports now send BPDUs and they act as a keepalive mechanism
- The new port roles are designated, root, alternate, and backup
- The new port states are forwarding, discarding, and learning
- The new port types are shared, edge (PortFast), and P2P
- When an RSTP port receives a legacy BPDU, it reverts back to compatible behavior and performance enhancement benefits are lost
- BackboneFast is configured on all switches in order to function in STP and UplinkFast is configured on access layer devices
Migrating
- You are not forced into removing the BackboneFast and UplinkFast commands – if they are left in place, they do not impact the operation of RSTP
- Removing the Uplinkfast command impacts the bridge priority and port cost values, so be sure you consider this
- CatOS (FLASHBACK!) does not permit the BackboneFast command within RSTP so you must remove it in that legacy case
- Plan a phased migration and use a maintenance window as traffic flows can be impacted
- The configuration of the features such as PortFast, BPDUguard, BPDUfilter, root guard, and loopguard are applicable in rapid-PVST+ mode also