Related Documentation
- QFX Series
- Example: Configuring Root Protection to Enforce Root Bridge Placement in Spanning Trees
- Example: Configuring Loop Protection to Prevent Interfaces from Transitioning from Blocking to Forwarding in a Spanning Tree
- Example: Configuring BPDU Protection on STP Interfaces to Prevent STP Miscalculations
- Understanding MSTP
- Understanding RSTP
- Overview of Spanning-Tree Protocols
- Understanding VSTP
Understanding Root Protection for STP, RSTP, VSTP, and MSTP
A Juniper Networks QFX Series product provides Layer 2 loop prevention through Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), VLAN Spanning Tree Protocol (VSTP), and Multiple Spanning Tree Protocol (MSTP). A loop-free network is supported through the exchange of a special type of frame called a bridge protocol data unit (BPDU). Peer STP applications running on the switch interfaces use BPDUs to communicate. Ultimately, the exchange of BPDUs determines which interfaces block traffic and which interfaces become root ports and forward traffic.
You can also see BPDUs generated when you run a bridge application on a device attached to the switch. This can interfere with root port election, which may sometimes lead to the wrong root port being elected through the above process. Root protection allows you to manually enforce the root bridge placement in the network.
Enable root protection on interfaces that should not receive higher-priority BPDUs from the root bridge and should not be elected as the root port. These interfaces become designated ports and are typically located on an administrative boundary. If the bridge receives more STP BPDUs on a port that has root protection enabled, that port transitions to a root-prevented STP state (inconsistency state), and the interface is blocked. This blocking prevents a bridge that should not be the root bridge from being elected the root bridge. After the bridge stops receiving more STP BPDUs on the interface with root protection, the interface returns to a listening state, followed by a learning state, and ultimately back to a forwarding state. Recovery back to the forwarding state is automatic.
When root protection is enabled on an interface, it is enabled for all the STP instances on that interface. The interface is blocked only for instances for which it receives more BPDUs. Otherwise, it participates in the spanning-tree topology.
An interface can be configured for either root protection or loop protection, but not for both.
Related Documentation
- QFX Series
- Example: Configuring Root Protection to Enforce Root Bridge Placement in Spanning Trees
- Example: Configuring Loop Protection to Prevent Interfaces from Transitioning from Blocking to Forwarding in a Spanning Tree
- Example: Configuring BPDU Protection on STP Interfaces to Prevent STP Miscalculations
- Understanding MSTP
- Understanding RSTP
- Overview of Spanning-Tree Protocols
- Understanding VSTP
