Hey all,
I’m working on a setup with two core switches (Core 1 and Core 2) running MLAG for redundancy and load balancing, and I’ve hit a weird problem with STP and MAC addresses. Hoping someone here can point me in the right direction.
The Setup:
- Core 1 and Core 2 are configured with MLAG (Multi-Chassis Link Aggregation) to handle traffic balancing and redundancy.
- Each core is supposed to have its own unique bridge MAC address. I manually set them:
- Core 1: 02:00:00:11:22:33
- Core 2: 02:00:00:11:22:34
- I’m running MSTP for Spanning Tree, and I’ve set Core 1 to have a lower STP priority (0x1000), so it should always be the root bridge.
The Problem:
After rebooting both cores, both switches end up using the same MAC address (Core 1’s MAC: 02:00:00:11:22:33), and both are claiming to be the STP root. This is “probably” creating some network instability.
Here’s what I’ve checked/done:
- The admin-mac is correctly set and auto-mac is disabled on both cores, so in theory, they should keep their unique MACs.
- I’ve verified all ports are in the forwarding state, and BPDUs are being exchanged.
- STP priority is properly configured, but Core 2 is still showing the same MAC as Core 1 and trying to become the root bridge.
Questions:
- Is this MAC address sharing normal in MLAG setups on MikroTik? I’m starting to wonder if this is intentional for MLAG to work and not a misconfiguration.
- How should STP be configured in an MLAG environment where both switches are acting as a single logical switch? Could there be some STP setting I’m missing that’s causing this root bridge conflict?
- Should I expect both cores to advertise the same MAC for the bridge interface when MLAG is active? Or should they each be keeping their unique MACs, and something else is going wrong?
I’m running RouterOS 7.14 on both switches. I feel like I’m missing something small but crucial here, so any advice or tips would be awesome.
Thanks in advance!