Switch stack uplink connectivity best practices

[Madura Malwatte]

Hi all,
I have some questions about uplink cabling from stack switches to upstream devices. In this scenario the stack switches are catalyst 9300's and upstream device are nexus 7k's in VPC.

Say the requirement is to have 4x10G uplinks per stack. Each stack can be either 5,6 or 7 switches per stack. What is the best practice to distribute the uplinks per stack?

For the example I have created below (stack of 6 switches) I have the uplinks distributed across 4 switches, with two uplinks to N7K A and another two to N7K B, and master and slave set to the remaining two switches which do not have any uplinks. Would this be the best way?

[Francesco Molino]

Hi

Don't recall any best practices about how to connect stack switches to upstream.

But I'll explain what I'll do:

- normally you configure your priority to your members to control which one would become matter in case of issues.

- based on this, I'll connect to upstream switches all members which can become master.

Then, on your example, I'll connect the master and slave and 2 more which can whoever you want to potentially become master

[Madura Malwatte]

Hi Francesco,

From the LAN deployment guide, it states "When three or more switches are configured as a stack, configure the stack master switch functionality on a switch that does not have uplinks configured." Hence why I am confused.

And any switch can potentially become master depending on how many switches fail, right?

[Francesco Molino]

Never noticed that documentation.

Anyway, if you have 3 members and you don't connect the master, if this one goes down, your master will be connected to the distribution.

Yes everyone can become a master depending on others fail. You leave them by default and an election will done or you can manage it using priority.

Also, sometimes, customers are connecting then with 2 links and they choose the first and last member of the stack.

You'll have 4 links bundled in lacp then the way you designed your connection is ok.

If you'll lose 4 members from your 6 , all your links  will go down but you'll have another issue ( 4 x 48 or 24 devices down).

[Deepak Kumar]

Hi,

I read this article But I am thinking that there are a lot of things the master switch is responsible for that could impact performance or avoid the non-trivial situation. Since I couldn't really think of any other relation between uplinks and master role, that was my conclusion.

Regards,

Deepak Kumar

[frank.bowrys]

Use the Best Practice guides, like the LAN connectivity one you mentioned and the Cisco Enterprise Campus Infrastructure Best Practice Guide.

With 5 or more switches in the stack, Cisco recommends that you statically number all the switches in the stack. Put your uplinks in the first switch and the last switch in the stack. Set those two switches as the two lowest stack priorities (1 and 2). In the middle of the stack, set your stack master to priority 15 and other switches in the stack down 1 incrementally. Set your MAC persistent timer to 0.

Frank