Catalyst 9500-24Y4C Core with virtual stacking design question

[thegreatone]

Hi everyone, we will be replacing our current core (4900M) and layer 2 switches (3750X) with C9500-24Y4C with advantage license and same for the L2 switches with another pair of C9500-24Y4C with essentials license. Currently we are doing HSRP on the cores for all SVI's. I was looking into doing stackwise virtual on the new cores instead to try to eliminate spanning-tree so wanted your opinions if that is something you recommend. Also, for the new L2 switches, since they don't have the advantage license I will need to set those up as standalone switches connecting back to the core so my question is that servers connecting to these will have one link going to each so will that cause any layer 2 issues since there isn't going to be any spanning-tree config? Thank you.

[justo]

Hi, the C9500-24Y4C is a great switch, and very competitively priced at the moment. I have deployed quite a few 9500's using stackwise virtual and had no issues. Keep in mind you will lose some of your ports for the stackwise virtual link, not like the old 3750's where you stacked at the back. So consider how many ports you will "actually" get.

To connect other L2 switches to the 9500 core, you would have a link going to both core switches in a port channel, so no spanning tree issues (but still configure spanning tree!)

Hope it helps,

Justin.

[thegreatone]

Hi Justin. Thanks for your reply. So, if a server has one link going to one L2 switch and another going to the other L2 switch, won't that be redunant? That's why I thought there would be some layer 2 issues. Would I then configure spanning tree on the layer 2 switches?

[justo · Accepted solution]

Would it be redundant? Most likely yes, but it only achieves redundancy, not so much throughput. Depending on how the server is setup it may only use one link at a time. and if one of your L2 switches fail, it would re converge to the other.

Spanning tree should be configured regardless of what you plug in. Without knowing the environment, the core should also have spanning-tree priority 0 for those vlans. Configuring spanning-tree properly (and understanding it) before you patch stuff in should be your #1 regardless of the platform.