I have a customer with a Nexus 5500 (N5K-C5548UP) running 5.2(1)N1(8a), which is old, I know. It has two 2000s (N2K-C2248TP-1GE) connected to it.
I wanted to convert the following interface to a trunk, but leaving the other side of the connection (a firewall) unchanged, so I can add sub-interfaces to that side without modifying the primary active untrunked interface. I have done this many times of the years and it generally works great. Here is the configuration before being modified:
interface Ethernet102/1/28 switchport access vlan 17 spanning-tree port type edge
Here are my initial changes:
switchport trunk native vlan 17 switchport trunk allowed vlan 17,517 spanning-tree port type edge trunk
Since the trunking mode is still access, nothing has changed from a practical standpoint yet, and traffic continues fine. But the thing that really makes the change go into effect is:
switchport mode trunk
For some reason at this point, I lose communication to the device plugged into Eth102/1/28, which is untagged on Vlan17. I don't know if it's a code issue, a FEX issue, or what. Any thoughts?
(of course, as cleanup I would remove the "switchport access vlan 17" but that is a mere remnant once the port is set to trunking).