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Questions about Stacking with stackwise cables and Link agg. groups

Hello /r/CCNA.

This is not a question where I am asking for the Exact CLI commands step by step but more of a high level overview question.

I have some questions about stacking on the back plane and utilizing regular static configured LAG (4x1GBps interfaces on each core switch)

I just was hired on this job a few months ago, and my boss told me that the two core switches in at our small business (under 100 employee's) are not stacked with a stacking cable.

They transfer data between each core switch via 4 x 1GBps interfaces (Gi0/17, Gi0/18, Gi0/47 and Gi0/48 bound as a single link)

Should i keep the LAG up AND utilize the stacking cable as well? Will that offer more bandwidth and more paths between the two core switches? Is it a good idea to utilize both?


should i just enabled the 10G SPF+ interfaces, plug in the stacking cables, reboot and then once i get master/slave going on the two switches REMOVE the static LAG after?

I think I should keep the LAG no? Because more paths and more bandwidth is better... right? :\

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Just 'cause it ain't in my flair doesn't mean I don't have certs
3 points · 9 months ago · edited 9 months ago

There's no reason to connect two switches of a stack together with ports on the front side in a Port Channel. The stackwise connection on the older switches was 32Gbps vs 4Gbps in your post. Additionally, if you had the stack cables become disconnected and they became two independent switches, you'd be pretty screwed if you were doing any layer 3 stuff as you'd have duplicate addresses, etc.

Just backup the configs on both, throw stack cables on the back, and call it a day if you want the high speed benefits. If you want the increased reliability (dual control planes), don't do that and do Etherchannel between the two at the cost of a lower throughput.

Edit: This applies largely to Cisco stuff, you're on your own to research how Dell does things, though it's probably similar.

Original Poster1 point · 9 months ago

Yes thank you for the input, that has really helped clear things up. I will start to bug some Dell Switch guru's and throw these questions their way.

Thank you again!

1 point · 9 months ago

Normally, stacking cables should offer pretty close to backplane speed, depending on the exact switch. This means it will always be much faster than any kind of physical interface combination since you remove the need to properly format everything, etc. Basically, it should completely bypass the buffer rings, which should give higher performance with stacking cables.

1 point · 9 months ago

This is not a question that has one answer.

We would need to know the topology of your network and the business use case. What are the objectives? Simplify the network? Ensure business uptime? Something else?

I personally would never use stacked switches for a Core in a business where uptime is critical.

If you're going to stack the switches, the LAG should be removed as it offers no benefits and the switches will not use it, they'll use the stack cable as the data path.

Stacking cables don't plugin to SFP+ ports, so I think there's some confusion going on here.

What switch model are we talking about?

Original Poster1 point · 9 months ago

OK so i'm CCNA . All my L2/L3 switches at home and both my routers are all Cisco.

However here at this job they use a mix of Cisco + Dell. So the core switches are Dell N1548 enterprise switches.

The CLI as well as the concepts look to be VERY similar or exactly like a cisco switch. (the web GUI is very strange to use)

The Stacking cables for this model switch say they go into the 10G SFP ports but maybe i read that wrong? Also the CLI to bring up the interface and assign it as a stack is:

stack-port tengigabitethernet 1/0/1 stack

(I know this is not a Dell Switch forum, but since I learned most of my networking skills here on /r/CCNA and since this was more theory and concept type question I thought it would be good to ask here on CCNA)

Original Poster1 point · 9 months ago

Also why would you not use stacking cables on core switches?

Just 'cause it ain't in my flair doesn't mean I don't have certs
1 point · 9 months ago

Because one light goes out, they all go out?

Stacked switches are more likely (to some degree at least) to fail together than non stacked switches. You also have fewer maintenance options to reduce downtime.

For instance, we had blade enclosures with 3120/3125s and we used to keep them in 2 stacks of 3 for those reasons.

1 point · 9 months ago

Stacks are generally for access layer because it simplifies management since it's all one logical switch.

The purpose of a Core should be reliability which means redundancy whether it be via FHRP, VSS, VPC, etc.

Stacking Core switches brings in the possibility of a problem with the IOS bringing down the entire stack.

Original Poster1 point · 9 months ago

Apparently Dell switches have this interesting feature called Non-Stop Forwarding which i just read about so i'm not sure if one of them goes down, do they both go down?

The Nonstop Forwarding (NSF) feature of your Dell N1500 series switch allows the forwarding plane of stack units to continue to forward packets while the control and management planes restart as a result of a power failure, hardware failure, or software fault on the stack master. This type of operation is called nonstop forwarding (NSF). When the stack master fails, only the switch ASICs and processor on the stack master need to be restarted.

I dunno if that means if one of them goes down that it won't bring down the whole network? i'm not too sure. I feel like my inital theory question was answered perfectly here.

Now i just need more understanding on how this will work on a Dell switch.

1 point · 9 months ago

The use case for NSF is if one switch goes down, the other takes over the active role. It is pretty popular and several vendors have it. It works, but you can still run into issues where a bug in the switch OS where it brings down both switches, NSF can't prevent that.

1 point · 9 months ago

It's very possible the Dell switches stack via the SFP, I don't have any experience with Dell Networking equipment.

Original Poster1 point · 9 months ago


but i accepted this mess. so now its my mess.

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