Cisco 9300 stack uplink design

[dm2020]

Hi All,

I have a quick question regarding switch stack uplinks. A customer has a stack of 8 x Cisco Catalyst 9300 switches but only two of the switches have 10GbE uplink modules installed which are currently  n switches 1 and 2 (which are also configured as the active and standby switches). The stack is then uplinked to a distribution switch using 2 x 10GbE links from each module in a port-channel.

This works but I'm wondering if the uplinks are optimal as it means that traffic from switches in the middle of the stack have to transit multiple hops before reaching an uplink. Does this matter or should I look at moving one of the uplinks to another switch in the stack?

thank you

[Dustin Anderson]

so, I doubt it matters, but I see your point. So is a 1/2 uplink assuming the ring is 1-8 then back to 1. This would have a hop of 3 max. 6>7>8>1 or 5>4>3>2 to get to an uplink.

Now, say you did 1/5 uplinks, you would only loose 1 hop as you would have 3>4>5 or 3>2>1 or 7>8>1 or 7>6>5

So, personally we went for cleanliness and have the fibers at the top of the stack.

[balaji.bandi]

I do not see any issue here, Switch 1 and Swtich 2 uplink to core or distribution is ok to be consider design.

[Leo Laohoo]

It won't make a difference. The speed of the stacking module is 480 Gbps.

Here's a nice (and crazy) hint:  If you've got a stack that big and only two uplinks, don't put any of the uplinks to the master switch.  Reason:  If the master switch should go crazy and reboots ...

[dm2020]

Hi All,

Thanks for the response.

Leo, regarding the recommendation of not connecting an uplink to the master switch for large stacks, is that something that is recommended by Cisco or is this something that you have experienced?

[Joseph W. Doherty]

I cannot say for the 9300 series, but it's something (not well known) Cisco recommended for earlier series. (The reason, I believe, it takes a bit of load off the master, which is managing the whole stack).

Also cannot say for the 9300 series, but earlier stack switches (to my knowledge) did not calculate shortest stack ring path to another member switch. I believe they just take the stack link's load into consideration, and shove traffic on them to keep them load balanced. If this is true for the 9300 series, where the uplinks are located within the stack might not matter, beyond perhaps being on the same switch (avoiding the stack ring, altogether).

[Leo Laohoo]

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@dm2020 wrote:

is that something that is recommended by Cisco or is this something that you have experienced? 

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It was discussed during a technical session in Cisco Live.  It sounded crazy but after much thought, it wasn't as crazy as it sounds.  

[balaji.bandi]

@Leo Laohoo  yes agreed.

another suggestion and alternative design, which make you confortable in terms of maintenance(add bit cost) but finally you are in good confortable way on this approach

split the stack in to 2, make 4 switches per stack, that way, failure domain reduced and you have each maintenance, rather all 8 need to go down if any emergency maintenance or software upgrade required.

[dm2020]

Thanks all, very helpful info.