The Juniper EX switch must be configured to enable BPDU Protection on all user-facing or untrusted access switch ports.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-253956	SRG-NET-000362-L2S-000022	JUEX-L2-000090	SV-253956r843901_rule	2025-03-07	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. BPDU Protection allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind interfaces that have BPDU Protection enabled are not able to influence the STP topology. At the reception of BPDUs, BPDU Protection disables the port and logs the condition.

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. BPDU Protection allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind interfaces that have BPDU Protection enabled are not able to influence the STP topology. At the reception of BPDUs, BPDU Protection disables the port and logs the condition.

ℹ️ Check
Review the switch configuration to verify that BPDU Protection is enabled on all user-facing or untrusted access switch interfaces. BPDU Protection discards all BPDUs received on a configured interface and stops forwarding on that interface. In contrast, Root Protection discards only superior root BPDUs but accepts remaining BPDU types. Verify BDPU Protection (bpdu-block-on-edge) and the edge interfaces where no BPDUs are expected. [protocols] mstp { bpdu-block-on-edge; interface <interface name> { edge; } } Note: Configuring BPDU Protection and Root Protection on the same interface is supported, but redundant because BPDU protection includes Root Protection. If the switch has not enabled BPDU Protection, this is a finding.

ℹ️ Check

Review the switch configuration to verify that BPDU Protection is enabled on all user-facing or untrusted access switch interfaces. BPDU Protection discards all BPDUs received on a configured interface and stops forwarding on that interface. In contrast, Root Protection discards only superior root BPDUs but accepts remaining BPDU types. Verify BDPU Protection (bpdu-block-on-edge) and the edge interfaces where no BPDUs are expected. [protocols] mstp { bpdu-block-on-edge; interface <interface name> { edge; } } Note: Configuring BPDU Protection and Root Protection on the same interface is supported, but redundant because BPDU protection includes Root Protection. If the switch has not enabled BPDU Protection, this is a finding.

✔️ Fix
Configure the switch to have BPDU Protection enabled on all user-facing or untrusted access switch interfaces. set protocols mstp bpdu-block-on-edge set protocols mstp interface <interface name> edge Note: Configuring BPDU Protection and Root Protection on the same interface is supported, but redundant because BPDU protection includes Root Protection.