MRP Loop Caused by PVST+ BPDU Flooding

Summary

When Metro Ring Protocol (MRP) is configured on ICX switches, PVST+ BPDUs received from a connected Cisco switch are not blocked by MRP ports, potentially causing Layer 2 loops.

Question

Why does MRP not block PVST+ BPDU packets?

Customer Environment

Customer Environment ICX switches configured with MRP and a Cisco switch running PVST+ connected to an MRP node.

Symptoms

MRP instability when clients are connected
CPU xSTP PDU counters spike
RHP drops and secondary port flapping between forwarding/blocking

Root Cause

PVST+ BPDUs (MAC 0100.0ccc.cccd) sent by a Cisco device trigger the ICX PVST+ auto-support behavior. Because 802.1w is disabled on MRP nodes, the ICX floods these BPDUs across the VLAN, effectively behaving like a hub and creating a loop within the MRP ring.

Troubleshooting Steps

show statistics cpu-pkt (check xSTP PDU counters)
Packet capture confirming BPDUs to 0100.0ccc.cccd

Workaround

Enable stp-protect on client-facing ports
Or enable pvstplus-protect (temporary client disruption may occur)

Resolution

Prevent PVST+ BPDUs from being forwarded into MRP nodes by applying STP/PVST protection on client-facing ports.

000006525

Article Number:
000012318

Updated:
May 08, 2026 02:33 PM (14 days ago)

Tags:
Performance, Ruckus ICX Switches

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