Stack uplink redundancy

[Justin Decker]

I'm building a new access layer switch on a collapsed core model, and I'm pondering what would be the best way to cable the uplinks. Most diagrams look like this:

SW1 -> Core1 SW1, Core2 SW1

SW8 -> Core1 SW2, Core2 SW2

However I was intrigued to notice one that looked more like this:

SW1 -> Core1 SW1

SW2 -> Core2 SW1

SW7 -> Core1 SW2

SW8 -> Core2 SW2

I'm thinking maybe this one offers more redundancy, but I'm not sure whether it is less efficient in terms of bandwidth. Can any experts comment on this?

[Masoud Pourshabanian]

The way you showed your connectivity is not obvious to me. Just to mention that the redundancy is not just cabling. Other factors are also involved. It is depending on your type of switches(nexus or traditional or stack-wise switches)

Your spaning tree configuration is also important in traditional swithches.

The common senario is connecting your core switches together with 2 or more links and connect ing your access switch to both of the core switches with at least one cable. Please explain what you have.

Masoud

[Justin Decker]

I'll be using VPC for this, so it's all LACP driven. Basically what I'm debating is the top vs the bottom approach in this diagram, as I've seen Cisco docs that allude to both (excuse my bad visio skills.) Minding of course to not place any uplinks on either the stack master switch or the hot standby switch.

The access switches are 2960-X's with FlexStack+, and the cores are Nexus switches.

[Masoud Pourshabanian]

I would go with the bottom approach. In terms of bandwidth, you get almost the same bandwidth in both approaches since there will be only one port channel and 4 members. In the top one, if you lose one of the switches with two uplinks, you will lose half of the bandwidth. Losing a switch is very likely. Last week , we lost two switch from 4 at the same time. Even add more link if you do not have physical constraint.

Suppose the stack switch like line cards for a chassis. Different line cards are used for creating port channels. The logic here is almost the same.

Masoud