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PRP, HSR & RSTP Capture Analyser

Check a substation network's redundancy from a capture: PRP redundancy trailers and supervision frames (LAN A / B mixing, lost frames, wrong LSDU size, nodes without supervision, RedBoxes), HSR tags (circulating frames, gaps) and RSTP BPDUs (root changes, topology changes, devices running their own spanning tree).

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Result

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Tool guide · know before you use

What this tool is, how it works and how far to trust it

An analyser for PRP and HSR redundancy (IEC 62439-3) and RSTP spanning tree, from a capture.

Read this before relying on a result. Every method, formula, assumption and limit is stated here, so you can check the answer yourself instead of accepting it blindly.

What it can do

  • PRP: per node, LAN identifiers, sequence gaps on this LAN, LSDU size, supervision frames and their interval, RedBoxes and their VDANs; LANs joined and A/B swapped.
  • HSR: frames seen twice at one port (circulating), sequence gaps, LSDU size.
  • RSTP: root bridge and changes, topology changes, legacy STP, devices running their own spanning tree, BPDUs from unknown devices.

Why you need it

  • Redundancy hides faults: a broken LAN, a cross-patched cable or a duplicate-handling error stays invisible until the second path fails.
  • Root changes and topology changes flush MAC tables and disturb GOOSE and SV.

Understand this first

  • PRP appends a 6-octet trailer (sequence number, LAN id A/B, LSDU size, suffix 0x88FB) and sends every frame on both LANs; the receiver keeps the first copy.
  • HSR inserts a tag (path, size, sequence) and sends each frame both ways round the ring; each node removes duplicates and its own frames.
  • Supervision frames (every LifeCheckInterval, 2 s by default) announce each node and its RedBox.

What you need before you start

  • A capture on one LAN (A or B) or one HSR port, at a mirror port.
  • Optionally the switch MAC addresses for the RSTP check.
  • A current browser (Chrome, Edge, Firefox or Safari). Nothing is installed and your data is never uploaded; it is processed on your own computer.

How to use it

  • Open the capture or load a sample.
  • Select the LAN the capture was taken on (or let the tool detect it).
  • Read the PRP, HSR and RSTP findings and node tables.

What you get

  • Findings and per-node tables for PRP and HSR, and a BPDU table for RSTP.

How to read the results

  • Frames with both LAN ids at one point: the LANs are connected — find the bridge.
  • A node's frames all with the other LAN id: its ports are swapped.
  • Frames passing an HSR port twice: a node is not removing frames — risk of a broadcast storm.
  • Root changes: correct the bridge priorities.

Technical basis

  • IEC 62439-3 frame formats (RCT, HSR tag, supervision TLVs 20/21/30/31); LSDU size checked against the frame length after the EtherType (and VLAN tag); IEEE 802.1Q BPDU format.

Limits: when not to rely on it

  • A capture point sees only the traffic forwarded to it.
  • PRP over VLAN-tagged frames and HSR quadboxes are decoded but not separately analysed.

Sample files for this tool

Download, open and compare with what the guide says you should see.

All sample files and what to expect →

For preliminary engineering use. Results must be checked by a qualified engineer against the project's standards. How results are checked · Terms & disclaimer · Build 0473054 · 2026-11-14