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Rapid Spanning Tree Protocol (STP) must be implemented at the access and distribution layers where Virtual Local Area Networks (VLANs) span multiple switches.


Finding ID Version Rule ID IA Controls Severity
V-66361 NET2004 SV-80851r1_rule Low
Spanning Tree Protocol (STP) is implemented on bridges and switches to prevent Layer 2 loops when a broadcast domain spans multiple bridges and switches and when redundant links are provisioned to provide high availability in case of link failures. Convergence time can be significantly reduced using Rapid STP (802.1w) instead of STP (802.1d), resulting in improved availability. Rapid STP should be deployed by implementing either Rapid Per-VLAN-Spanning-Tree (Rapid-PVST) or Multiple Spanning-Tree Protocol (MSTP), the later scales much better when there are many VLANs.
Network Infrastructure Policy Security Technical Implementation Guide 2019-03-12


Check Text ( C-67007r1_chk )
In cases where VLANs do not span multiple switches it is a best practice to not implement STP. Avoiding the use of STP will provide the most deterministic and highly available network topology. If STP is required, then review the switch configuration to verify that RSTP or MSTP has been implemented. Following are example configurations:


spanning-tree mode rapid-pvst


spanning-tree mode mst
spanning-tree mst configuration
name Region1
revision 1
instance 1 vlan 10, 11, 12
instance 2 vlan 13, 14

If RSTP or MSTP has not been implemented where STP is required, this is a finding.

Note: Note: Cisco has implemented RSTP as part of MSTP and Rapid-PVST+.
Fix Text (F-72437r1_fix)
Configure Rapid STP be implemented at the access and distribution layers where VLANs span multiple switches.