Transition from Layer 3 to Layer 2 Port-Channel

[ChristopherKirwan88876]

Hey guys,

So currently I have a core switch that's catOS using a layer 3 port-channel to two nexus 5K's.  I want to change this to a layer 2 port-channel.  In doing this I've created a new routing vlan, and a new port-channel.  However I wanted to test that the port-channel would come up before the official down time, so I was thinking of running new cables and connecting the layer 2 port-channel ahead of time.  Currently the two Layer 3 PC's are separate, one for each 5K coming off the core.  Do not ask me why I inherited this network a month ago.   My questions are:

1. Will this cause spanning-tree issues?

2. Will this cause routing issues?

I uploaded a drawing for a visual.  The downtime is on Sunday and today is my last day in the office.  Quick responses welcome.

[Reza Sharifi]

Hi,

Are the 5ks in VPC mode? if they are not, you can't do this. The diagram does not say anything about VPC.

HTH

[ChristopherKirwan88876]

Yes they are in vPC mode.  There are vPC running currently just not these layer 3 port-channels.  What are you saying can't be done?

[Reza Sharifi]

What are you saying can't be done?

I was trying to say that if the 5ks are not vPCed together, you can't create a Portchannel from the core to 2 different 5ks but since you have the 5ks connected together in vPC mode, you should be fine.

HTH

[ChristopherKirwan88876]

Thanks, so then if I have the layer 3 port-channels up at the same time as the layer 2 there wont be spanning-tree or routing issues?

[balaji.bandi]

When you running already vPC, what is the use case of adding another Layer 3 Po here, trying to understnad, so we can advise better, if this resilaince purpose add same Link to exiting vPC ?

[ChristopherKirwan88876]

The issue is currently there is a layer 3 port-channel and I want to change it to layer two.  I want to go away from the layer 3.  

[Reza Sharifi · Accepted solution]

Should no be an issue. Build the layer-2 PO ahead of time and keep in down state. In a maintenance window, bring it up and make sure both physical interfaces come up. Once you are done with testing you can shut down the PO again and in another maintenance window being up the PO again and disconnect the layer-3 links. You can also do everything in one maintenance window if it is long enough for both testing and migrations.

HTH

[ChristopherKirwan88876]

Awesome thanks for your help.  We have an 8 hour window where we're upgrading the 5K software so hopefully by the end I will have time to do this.

[Reza Sharifi]

Yes, defiantly 8 hours is long enough to upgrade the 5ks and do the migration from L3 to L2. You can do a whole a lot ahead of the window, as they are not disruptive to production. Here are a few items to works on before the window starts:

Figure out what software you will be upgrading to on the 5ks.

Read the release notes carefully for the version you are upgrading to.

Make sure you don't need to do multiple upgrades (path upgrade).

Load the software on the switches

Build the PO and keep it in down state

overall, the 5ks upgrade should not take more than an hour and if you get everything else ready, you should be able to do it all in about 2 hours and spend another 30 min for testing and verification.

Good Luck!

HTH