Edge switch redundancy to two core switches

[RyanPowers9691]

I want to provide best redundancy for an access switch (Cisco 3650) when connecting to two core switches (Cisco 9500 series), as show in attached topology. My plan is to configure 2 uplinks on the 3650, one to each core switch. My question is, should I configure the 2 uplinks as a port channel? Or should I just leave them as two separate links and ensure STP blocks one? What are the pros/cons of each option? Is there another option entirely that I'm not thinking of?

[Joseph W. Doherty]

You can only port channel if cores are one logical device, e.g. stacked, VSS, vPC.

If you can port channel, often considered a better choice.

[Joseph W. Doherty]

Prior assumes L2.  If L3 edge, you can route on both links, concurrently.  (3650 is also a L3 switch.)

[RyanPowers9691]

So, would you suggest best method to be stacking the 9500 switches as VSS, then creating port-channel with the two uplinks? My end goal is to have the best topology for redundancy and availability 

[Reza Sharifi · Accepted solution]

So, would you suggest best method to be stacking the 9500 switches as VSS, then creating port-channel with the two uplinks?

Yes, that is correct. configure the 9500 as VSS, create a portchannel from the access switch, and put both links in that portchannel. This design will give you uplink as well as core switch redundancy.

HTH

[Joseph W. Doherty]

I often would suggest stacking/VSS (don't recall which they support) the 9500s, but whether that's the "best", hmm, there are arguments against, especially versus using all L3.

One principle argument against using stacking/VSS, as the devices are so tightly bound together, possible some form of bug or issue will take down the one logical device.  Keeping devices independent, whether via L2 or L3, keeps their IOSs independent too.  For example, you could run two different IOS versions on the two devices or even use two different device types.  Again, the idea is the difference, hopefully, precludes one single issue/bug taking out the whole core.

Possibly, some of that "thinking" goes into the Nexus series using their vPC approach, where a pair of devices aren't quite as tightly coupled.

[Leo Laohoo]

There is no real "right answers" here.  To VSS or not to VSS is neither wrong nor right. 

Half of our 9500 are in VSS and the other half are not.  We deliberately did that because past experience have dictated that VSS is not entirely reliable nor stable.  

[Joseph W. Doherty]

Ah, nice, a real world example of using and not using VSS; especially doing about half each way.

"We deliberately did that because past experience have dictated that VSS is not entirely reliable nor stable."

BTW, that with VSS regardless of platform and/or IOS version, or 9500s in particular?

[Leo Laohoo]

IOS only