Nexus 2248 and Layer 2 or layer 3 ports

[stephen.ehlas]

Hi

This may seem like a silly question, but it is one that has been vexing me for a few days.

So, my ESX servers need layer 2 adjacency to vmotion. I have a Nexus 2248, downstream from a Nexus 5548. The Nexus 5548 has a L3 routing module in it. I know that the L3 module converts the whole nexus setup to a routed mode

So, the question is - Can I use the "no switchport" command to make L2 ports on the nexus 2248 for the ESX adjacency? Or is there another command I eed?

Or do I need to connect the vmotion port to a seperate c3750 just to create a L2 adjacency?

[David Lucas]

Hello Steve,

I'm not sure I follow what you are attempting to accomplish.

You are correct in that when you add a Layer 3 module to the Nexus 5500 switches that it allows it to route traffic. There is a 160 Gig channel that connects the module to the Nexus 5500.

I'm confused about this question though:

"Can I use the "no switchport" command to make L2 ports on the nexus 2248 for the ESX adjacency?"

When you do "no switchport" on any Cisco switch (assuming it supports routing) then you've made that interface a Layer 3 routed port. It sounds like you are trying to do Layer 2 to your ESX server for VMotion (which last I knew was a requirement for VMotion). If you want to do layer 2 you just need to place that interface in the correct vlan and make sure you set spanning-tree configurations appropriately.

To the best of my knowledge, routed ports are not supported on FEX interfaces today.

Let me know if this helps.

Dave

[stephen.ehlas]

Hi David

Thanks for the quick reply.

I was under the impression that the nexus 2248 is a line card extension of the 5548. So when the Layer 3 module is installed in the 5548 it also effects the 2248 - but you are saying that this is not true?

[David Lucas · Accepted solution]

Hello Steve,

You are correct that a FEX is a line module to the Nexus 5500, but just like any other chassis based switch you can do layer 2 and layer 3 in the same switch.

The one slight difference when you insert the layer 3 module, the number of FEXs that can be supported drops. Without the Layer 3 module installed we support 24 FEXs, when you install the module we only support 16.

http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/configuration_limits/limits_521/nexus_5000_config_limits_521.html#wp328407

By the way, if the module is inserted but not being used (no layer 3 interfaces), then the number of FEXs is still 16.

FYI, the number FEXs is based on code level. This example is with Configuration Limits published for 5.2.x code. To be certain refer to configuration limits for your release.

Hope this helps!

Dave

[stephen.ehlas]

Hi Dave

Thats cool - thanks for the answers

Regards

Steve