Unnecessary uplinks from switch stack to MX68-HA?

[henleyjj]

Hi, I have a design question. 

We're planning on deploying 2 x MS210-24P (stacked) with 4 x uplinks to MX68-HA pair (see diagram below).

However, I thought the number of uplinks maybe that would be unnecessary since the switches are stacked.

And would be better off with 1 uplink from each stack member to each MX68? What do you guys think?

[cmr]

@henleyjj Only 1 uplink from each switch in the stack will be active at one time, but you can link both to both as you have suggested. 

We originally set up all of our sites with only one link to each MX and then started adding a second, but stopped as it did create some spanning-tree issues where we had MS and MX.  Therefore on the dual linked sites we commonly left the second link port disabled, so it could be activated in an emergency, but wouldn't stop the switches coming back up after a reboot.  This has since been resolved but we have left it as it is with some single linked and some dual linked...!  

The sites that had Cisco IOS switch stacks with MX were fine.  

The only issue that you might experience with the single linked option is that if one switch went down, you could end up with the MXs operating in dual master mode and you don't want that. 

[KarstenI · Accepted solution]

Having two links from each MX is the "official" way to do it:

https://documentation.meraki.com/MX/Deployment_Guides/MX_Warm_Spare_-_High_Availability_Pair#Recomme...

But as @cmr mentioned, take care of spanning tree. You have to make sure that BPDUs that are sent from a switch to the MX are sent back over the second link. You are not allowed to drop untagged frames. If you use VLAN 1 untagged in your environment you are fine.

[henleyjj]

Thanks all. We decided to leave it as is. Yep we'll definitely be not dropping untagged frames.

[PhilipDAth]

From the MS120s to the WAN interfaces, good.

On the LAN side, I only ever use a single link to each MX.  No loops.  Rock-solid reliable.