| Explanation & Hint:
The two types of Spanning Tree Protocols that can cause suboptimal traffic flows because they assume only one spanning-tree instance for the entire bridged network are:
- STP (Standard Spanning Tree Protocol): The original Spanning Tree Protocol, as defined in IEEE 802.1D, creates a single spanning-tree instance for the entire network, regardless of the number of VLANs. This can lead to suboptimal paths in networks where multiple VLANs are configured, as it doesn’t allow for load balancing across different VLANs.
- RSTP (Rapid Spanning Tree Protocol): Although RSTP (IEEE 802.1w) is an evolution of STP that provides faster convergence, it still operates a single instance of spanning-tree for the entire network. Like STP, RSTP does not create separate spanning-trees for each VLAN, which can lead to suboptimal traffic flows in networks with multiple VLANs.
On the other hand:
- PVST+ (Per VLAN Spanning Tree Plus) and Rapid PVST+: These are Cisco enhancements to STP and RSTP that maintain a separate spanning-tree instance for each VLAN. This allows for more optimal traffic flow as it can balance load across different VLANs.
- MSTP (Multiple Spanning Tree Protocol): Defined in IEEE 802.1s, MSTP also allows for multiple spanning-tree instances but groups VLANs into instances, providing a balance between single-instance STP/RSTP and one-instance-per-VLAN PVST+/Rapid PVST+. This can be more scalable than PVST+ in large networks with many VLANs.
Therefore, STP and RSTP are the protocols that would fit the criteria of assuming only one spanning-tree instance for the entire bridged network, potentially leading to suboptimal traffic flows in a VLAN-rich environment. |