LACP between switch stack and MX

Comes here often

LACP between switch stack and MX



I have 2 MX devices (warm spare) and 3 switch stack (MS, physically stacked with stack cable).

Do I need to enable Link Aggregation on stack connected to MX (to aggregate 3 ports)? 

At the moment 1 ports from every switch is connected to 1 MX and same for a 2nd MX. On every MX 3 LAN ports are used for switches. STP is disconnecting 2 (as it should I believe), meaning only 1 port is active at given time.


If I need, how to enable LACP on MX as I see no option to do so? And to my knowledge it should be done on both sides for link aggregation to work (maybe...? 🙂 )


Thank you





Kind of a big deal
Kind of a big deal


Mx cant do lacp 

I would use 1 or 2 cable from each stack to each mx. (always use stp on this switch ports)

Comes here often

That's a shame...


So if I were to have stack of 7 switches (let's say), only one uplink would work while 6 ports were off.. not great..



Kind of a big deal

That's correct. 1 port would be active, any others would be STP disabled unless the active one fails.

I may we'll be wrong but I would guess a 7 switch stack with Meraki is a bit of an edge case. That would be a lot of east-west traffic.

Comes here often

Yep, that's why I thought of using all links at the same time rather than limit to one.

Well it is what it is 🙂



Bear in mind that (somewhat model-dependent) your MX is probably unlikely to be able to process the load from a whole bunch of high-capacity links anyway, particularly if you have Advanced Security and/or VPN functions running.   If it's a 'big' MX (250? 450?) then the bottleneck probably moves to your Internet link(s), so those high-capacity uplinks will likely be under-used.   If a large proportion of your traffic is east <-> west, then you're probably best with an aggregation switching layer and routing there (in ASIC)

Good point here. I use MX84+VPN, so far, highest load I saw on MX was about 50% (peak)

Kind of a big deal

I'm sorry but using the high capacity traffic is not the main reason why we would want to use lacp port channels on the MX.


We need port channels on MX for a more stable spanning-tree setup.  Since the MX does not support STP which is actually should we have to rely on the bounced back STP messages coming from the switch to have the higher portnumber blocked.


I would much rather have the MX at least support STP and even better support LACP so the MX natively takes care of those layer 2 messages to have a more stable topology.

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