Stacking issues

[Chris_Durham]

I am currently implementing a new Meraki network and we have 3 MS225 switches in a stack configuration. We have a single uplink (at the minute, more will come as we free up ports on the core switch) The uplink is connected to one of the SFP+ ports on switch 1. I connected a test pc to switch 3. I was able to initiate connections outbound from the test pc to the rest of the network but could not connect inbound. The test pc is on VLAN 2, VLAN 1 is used for management traffic and server traffic. I tried to ping the test pc from the Meraki dashboard Tools section of each switch in the stack and none of them could get a response. I moved the test pc to switch 1 (the one with the uplink) and repeated the ping tests and all 3 switches can now ping the test pc and also other systems on the network can now initiate remote connections to the test pc. 

I don;t have an issue putting uplinks into each switch but my understanding was that it is not strictly necessary as the stack will transfer the connection correctly. If this is not the case then surely the stacking cable is pretty pointless? 

How critical is the ordering of the stacking cables? The documentation says to go sw1 port 1 to sw 2 port 2, sw2 port 1 to sw3 port 2 and sw3 port 1 to sw1 port 2. I will check the cables next time I am onsite but could this behaviour be caused by the stacking cables being incorrectly routed?

[DarrenOC]

hi @Chris_Durham 

Sounds like you've read the stacking documentation as you're following the below physical setup:

You don't require an uplink per switch to your core but best practice to have more than one uplink per stack.  If you lose the top switch lets say traffic will flow via the stack out the bottom switch uplink.

[Chris_Durham]

Hi, 

[Chris_Durham]

Hi, the intention is to put more uplinks in, but the issue I have is that a device connected to a switch without an uplink seems to only have 1 way communication - it can communicate outbound from the stack but neither the stack nor anything else on the network can initiate a connection to that device. This means that if we lose the uplink for a particular switch then any devices on that switch will no longer communicate correctly. 

[Chris_Durham]

I have checked the cables and they are correctly connected to each switch

[DarrenOC]

check your uplink configuration on both sides.

[Chris_Durham]

Hi Darren, So the uplink is possibly the issue then - I have configured it as an aggregate link but because of delivery delays on the transceivers we only have 1 link actually in place. config is as follows 

sw1 port 51 and 52 are aggregated

core sw1 port 3 and core sw2 port 3 are aggregated and both core sw are stacked (MS425 using 40Gb ports for stacking)

only sw1 port 51 is connected to core sw1 port 3 

Again though if it was an issue with the aggregate link then that would destroy it's usefulness for failover! 

[Chris_Durham]

I should also say that both ends are configured as trunk ports, native VLAN 1 and all VLAN's allowed

[DarrenOC]

That's what I was after - so both sides are configured as Trunks - same Native VLAN and all VLAN's allowed - TICK

Spanning-Tree - what does your core consist of - is it Meraki?  Is it set as the lower priority to your new switch stack?  Anything showing in event log in the dashboard?

[Chris_Durham]

yes - core is 2 Meraki MS425-16's, RSTP is enabled on the uplink - it is enabled on all ports by default so I've just left it alone. How would I check the priority ? can't see anything about it on the dashboard. There is nothing in the logs other than the expected port up/port down messages when the test pc was plugged in and then moved. There is a message that the port STP status changes from disabled to designated when the test pc was plugged in. 

[DarrenOC]

On your dashboard. Switch > Configure > Switch Settings

[Chris_Durham]

Ok - I haven't set any priority. I guess my MS425 stack should be the root of the tree and have the lowest priority then? The MS425 stack does the layer 3 routing. 

[ww]

Did you update all switches prior to creating the stack?

Did you try rebooting switch 2 and 3?

[Chris_Durham]

No - stack was created before the switches where connected, All switches running current firmware and yes all switches where rebooted last night

[DarrenOC]

👍

Quite a big change to make during working hours on a live network but yes - make the MS425's your root.

[KRobert]

Hi @Chris_Durham,

I was just working with the MS Switch Stacks recently so I think I know what the issue is. You stated the stack was created before the switches where connected. That is your issue. If you look at the switch stack config documentation, there is kind of a process with the stack setup.

https://documentation.meraki.com/MS/Stacking/Switch_Stacks

The steps below explain how to prepare a group of switches for physical stacking, how to stack them together, and how to configure the stack in Dashboard.

1. Add the switches into a Dashboard network. This can be a new Dashboard network for these switches, or an existing network with other switches. Do not configure the stack in Dashboard yet.
2. Connect each switch with individual uplinks to bring them both online and ensure they can check in with the Meraki Dashboard.
3. Download the latest firmware build using the Firmware Upgrade Manager under Organization > Monitor > Firmware Upgrades, if they are not already set for this. This helps ensure each switch is running the same firmware build.
4. With all switches powered off and links disconnected, connect the switches together via stacking cables in a ring topology (as shown in the following image). To create a full ring, start by connecting switch 1/stack port 1 to switch 2/stack port 2, then switch 2/stack port 1 to switch 3/stack port 2 and so forth, with the bottom switch connecting to the top switch to complete the ring.

Step 4 includes the image @DarrenOC provided and continues through the steps on how to setup the stack.

I tried the same thing you did my first time setting up the stack and I had all kinds of issues. If you follow the documentation it should come up for you and then you'll be able to use 1 uplink for the stack (multiple is better as others have pointed out). 

Hope this helps. 

[Chris_Durham]

Good Morning Everyone,

I'm not entirely certain which of your great suggestions solved this issue but it is now working. I changed the STP priority of my main MS425 core stack to be 0 to make it the root of the spanning tree. I also put the second uplink in place to complete the link aggregation. I have tested removing each of the uplinks and it still works as I would expect it to. 

Changing the STP root did change the topology map overnight to put the core stack at the root of the network so perhaps it was that that was causing the issue. 

Anyway it's working now so thank you all for your input on this. 

Chris

[DarrenOC]

Morning @Chris_Durham 

Great to hear the issues resolved. 

enjoy the rest of your day.

[KRobert]

Glad it is working!