The Arista MLS layer 2 switch must have BPDU Guard enabled on all switch ports connecting to access layer switches and hosts.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-255971	SRG-NET-000362-L2S-000022	ARST-L2-000060	SV-255971r882255_rule	2025-02-20	2

Description
If a rogue switch is introduced into the topology and transmits a Bridge Protocol Data Unit (BPDU) with a lower bridge priority than the existing root bridge, it will become the new root bridge and cause a topology change, rendering the network in a suboptimal state. The STP PortFast BPDU guard enhancement allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind the ports that have STP PortFast enabled are not able to influence the STP topology. At the reception of BPDUs, the BPDU guard operation disables the port that has PortFast configured. The BPDU guard transitions the port into a disabled state and sends a log message.

Description

If a rogue switch is introduced into the topology and transmits a Bridge Protocol Data Unit (BPDU) with a lower bridge priority than the existing root bridge, it will become the new root bridge and cause a topology change, rendering the network in a suboptimal state. The STP PortFast BPDU guard enhancement allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind the ports that have STP PortFast enabled are not able to influence the STP topology. At the reception of BPDUs, the BPDU guard operation disables the port that has PortFast configured. The BPDU guard transitions the port into a disabled state and sends a log message.

ℹ️ Check
Review the Arista MLS to verify that BPDU Guard is enabled on all user-facing or untrusted access switch ports. switch#show run \| section bpdu interface Ethernet37 spanning-tree bpduguard enable If the Arista MLS switch has not enabled BPDU Guard, this is a finding.

✔️ Fix
The Arista MLS switch provides the capability to configure "spanning-tree bpduguard". Configure the Ethernet interface commands: config interface Ethernet[X] switch(config)#interface ethernet [X] switch(config-if-Et[X])#spanning-tree bpduguard enabled switch(config-if-Et[X])