MS425, 2x2 Stack or 1x4 Stack

[PaulM2]

Evening All,

Got a project coming up that is fairly simple, yet fairly large. There are roughly 55 IDFs each with a single switch in. 2 with large stacks 4/8 switches.

Each IDF with a single switch will have 2 MMF uplinks for redundancy to core. So in total, roughly 110 SFP+

At the core I have 4 x MS425-32 switches going in. What I can’t decide on is whether to have:

A) 2 stacks of 2 x MS425 (core stack 1 and core stack 2) with an uplink from each idf to each core stack.

B) 1 stack of 4 x ms425 (core stack) with an uplink from each idf going to 2 separate switches in the stack.

There isn’t any east-west traffic, so no SVI’s. VLANs all terminate on upstream MX.

Can anyone suggest any pros/cons to either method?

All I have so far is with 2x2 stack I can stage firmware rather than bringing the entire 1x4 offline. Or if I use 1x4 I don’t have to worry about linking them aside the stack cables.

I hope this makes sense, I am aware I need sleep! Any insight is greatly appreciated.

[Brash]

Either way will work.

A few things to consider:

• As you mentioned, when upgrading a switch stack, all switches in the stack will reboot at the same time. 
• With two separate switch stacks, you're relying on STP to prevent loops.
• With two separate switch stacks you technically have a greater spread of traffic and bandwidth up to the MX 

[cmr]

If you have enough ports, which it looks like you might, then I'd go with 2x2 for upgrade flexibility, where in theory you'll never take the IDF switches offline for more than a few seconds whilst spanning tree converges.  Make sure the 425s have a much lower bridge priority than the edge switches! You'll need a fast cross stack link as all traffic to the upstream MX will go via one stack with the other only reaching it via the first.

[PaulM2]

I plan on connecting each Stack to each HA MX, so traffic shouldn't have to traverse stacks to hit the MX. I figure i'll connect stack 1 / stack 2 with either 2 or 4 10Gbps LAG's to provide 20Gbps / 40 Gbps bandwidth in event it happens.

I still can't find any solid reason to prefer one over the other other than firmware upgrades.

[cmr]

Only one stack will talk live to the MXs unless you don't link the stacks as it should prefer the LAG.  The only control is spanning tree, unless you have different VLANs on each stack, which I wouldn't recommend...

[PaulM2]

Of course, my error. So I guess my decision is down to bandwidth between all 4 switches, vs firmware upgrade resiliency.

[DarrenOC]

Just to add to the discussion - by introducing the 2 x 2 switch stack you are added a level of complexity to the design that doesn't really need to be there.  Is the business a 24 x 7 operation 365 days of the year so can't afford any downtime to upgrade the cores?  As already highlighted, you also don't gain anything by having the dual stacks as only one will pass traffic to the MX due to STP.  I believe in keeping it simple unless the business requirements stipulate otherwise.

[PaulM2]

To be fair, it is a hotel so operations are 24/7/365, but that's not to say that downtime can't be arranged. The firmware staged upgrades is really the only difference and it's such a small matter I am inclined to agree that a the 1x4 is the better options.

[PhilipDAth · Accepted solution]

It is always tough when you have two correct solutions.

So this is a "IMHO".  If the site is not 24x7, and you can schedule in an hour of downtime every 6 months for firmware upgrades, I would go with a single stack of 4 switches.  I would choose this option because it has less complexity.