SLX MCT with RSTP

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2-SLXs running R-Code with MCT and RSTP between them.  Both SLXs are set for Root Bridge Priority 0.  One of the SLXs is the Root of the bridge and the other SLX shows Rootport towards the Root Bridge which in a typical switch environment I would expect; but in other vendors implementations of MLAG,MC-LAG,VPC I have seen that both devices would both appear to be root bridges (acting as a single shared common Root Bridge Identifier). 

Is this the expected behavior with MCT and RSTP where each SLX device is running independent spanning-tree?

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paulcian

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Posted 3 weeks ago

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Tomasz

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Hi Paul,

Do you mean RSTP for entire traffic or just data VLANs?
Phew, the number of those approaches is brain-splitting.
In theory, I believe STP from a downstream device should treat the LAG (terminated in both MLAG peers) as a single L2 link (so MLAG peers should be treated as a single device from STP perspective).
But you shouldn't run STP on your MLAG links IMHO. MLAG has it's own option for getting safe from the broadcast storms without blocking any links for known unicast traffic.
Also make sure your peer link control VLAN (ISC, IST etc.) doesn't get blocked by STP anyhow. I'm not yet familiar with SLX MCT but if it works like with others if you block the control connection between peers, your MLAG is not working in fact.

Regards,
Tomasz