Enabling uplink ports disrupted network

[Phil.Males]

I looke around and can't find the answer so ill ask here. I have a pair of UCS-FI-6248 and was starting to set up a disjointed network. The only thing I had done was run the cables to the FI's and enabled the ports, as soon as I did I started getting alerts from some VMs losing connection and noticed my VMWare hosts had lost communication. I had not configured any port-channels, vnics, vlan groups for this new connection all I did was enabled the ports. In my current setup, I have a port-channels and all my vlans are globally configured and assigned to the vnic templates. I might be missing something and any ideas on what I did or didn't do would be greatly appreciated.

I did this on another UCS domain and did not have this problem, but don't remember if I had already set the vlan group to the port-channel or enabled the ports first. 

Thanks

[Kirk J]

You want to configure your vlans, and assign the vlans to the specific port/port-channels prior to enabling a port that has a connection.  The designated receiver role for a given vlan will get chosen from the available logical uplinks, and if that includes your connection to no where (as far as that vlan is concerned) because you haven't pruned off the vlans, your ARP and broadcasts will no longer function.

You have a 50/50 chance (for 2 logical uplinks) that the uplink chosen for a given vlan's DR will be correct.

We frequently see customers with incorrect disjoint layer 2 configs that worked for a while, whose issues didn't show up until the ports were flapped, at which point the vlan(s) DR role was reevaluated and assigned to an unintended port.

Kirk...