Host must filter Bridge Protocol Data Unit (BPDU) packets

MediumLevel 1Automatedvmware

Description

To prevent cascading lockout of uplink interfaces from the ESXi host, the Net.BlockGuestBPDU parameter can be set to 1, enabling BPDU Filter to drop BPDU packets sent from virtual machines to the physical switch. This is crucial as ESXi's Standard and Distributed Virtual Switches do not support STP, making them prone to network loops if BPDUs are unfiltered. The audit reads Net.BlockGuestBPDU with esxcli and requires 1. Runs in the ESXi Shell (busybox sh) as root.

How it is checked

Audit method: Shell command

shell

out=$(esxcli system settings advanced list -o /Net/BlockGuestBPDU 2>/dev/null) || exit 1
v=$(printf '%s\n' "$out" | awk '$1=="Int" && $2=="Value:" {print $3; exit}')
case "$v" in ''|*[!0-9-]*) echo '/Net/BlockGuestBPDU: no integer value'; exit 1 ;; esac
if [ "$v" -eq 1 ]; then echo compliant; else echo "/Net/BlockGuestBPDU = $v (expected 1)"; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

From an administrative PowerCLI session: Execute - Get-VMHost | Get-AdvancedSetting -Name Net.BlockGuestBPDU | Set-AdvancedSetting - Value 1 -Confirm:$false. Validate network appliances/virtual switching workloads before enforcing this setting.

Properties

Operating systems: Any
Tags: vmwareesxinetwork
Reference: CIS VMware ESXi 9.0 Benchmark v1.0.0 - 5.4 Host must filter Bridge Protocol Data Unit (BPDU) packets

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target vmware