STP Loop Detector

Spanning-tree topology change forensics: TCN flood detection, root bridge verification, blocked port audit, BPDU guard/filter violations, PVST+ inconsistency across VLANs, and loop-risk scoring.

Cisco IOS/NX-OS

Arista

HP/Aruba

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Capabilities

TCN rate & source tracking
Root bridge per-VLAN verify
Blocked port inventory
BPDU guard violation log
PVST+ VLAN inconsistency
Port-fast on trunk detection
Loop risk score 0–100

Required inputs

Parameters the script accepts. Defaults shown; some are vendor- or context-gated.

Parameter	Type	Default	Notes
Expected root bridge MAC expected_root	string	—	—
TCN alert threshold /min tcn_threshold	number	5	—
Check PVST consistency check_pvst	bool	true	—
VLAN range to check vlan_range	string	1-4094	—

Hint 1 — Name your vendors and OS versions

Mention the exact platforms you run (Cisco IOS/NX-OS, Arista, HP/Aruba) so the generated fault logic uses the right CLI/NETCONF syntax.

Hint 2 — State your real thresholds

Provide concrete values for Expected root bridge MAC, TCN alert threshold /min, Check PVST consistency instead of the defaults — they shape what counts as a fault.

Hint 3 — Prioritize the checks you need

This tool can tCN rate & source tracking and root bridge per-VLAN verify. Ask for the subset relevant to your incident to keep output focused.

Hint 4 — Describe your inventory format

Tell the assistant whether your device list is CSV, YAML, or JSON and which columns it has, so parsing matches your data.

Sample inventory schema

Authoritative shape of the device/policy data this script consumes.

switches.csv

csv

12 dist+access switches across two DCs (Cisco + Arista)

terminal

hostname,mgmt_ip,site,role,vendor,os,stack_size,vlan_count,uplink_speed
dist-sw-01,10.40.0.11,LON1-DC,distribution,cisco,iosxe-17.9,1,148,40G
dist-sw-02,10.40.0.12,LON1-DC,distribution,cisco,iosxe-17.9,1,148,40G
dist-sw-03,10.40.0.13,FRA1-DC,distribution,arista,eos-4.31.2F,1,124,40G

expected_roots.yaml

yaml

Per-VLAN-range root/secondary expectations + BPDU-guard policy

yaml

# Per-VLAN expected root bridge (used for primary/secondary verification)
expected_roots:
  - vlan_range: 10-99      # user VLANs
    primary: dist-sw-01

Expected output

Reference terminal output the script should produce — used as a stylistic and structural target.

terminal

[14:45:11] STP topology analysis — 12 switches, 47 VLANs

ROOT BRIDGE VERIFICATION
  VLAN 1:    Expected 00:1A:2B:3C:4D:5E  |  Actual 00:1A:2B:3C:4D:5E  ✓
  VLAN 100:  Expected 00:1A:2B:3C:4D:5E  |  Actual AA:BB:CC:DD:EE:FF  ✗ MISMATCH!
  VLAN 200:  Expected 00:1A:2B:3C:4D:5E  |  Actual 00:1A:2B:3C:4D:5E  ✓

[CRITICAL] VLAN 100 root bridge mismatch!
  Expected: core-sw-01 (00:1A:2B:3C:4D:5E)
  Actual:   access-sw-07 (AA:BB:CC:DD:EE:FF) — rogue root detected