Regarding the error you are experiencing: the first thing I would personally start searching for is whether there is a native VLAN mismatch or a cabling fault where some other VLAN leaks into the VLAN 20.
The message is somewhat cryptic: it tells you that the switch received a Cisco PVST or RPVST BPDU (which is addressed and encapsulated differently than IEEE STP/RSTP BDPUs) but this BPDU was missing a Cisco proprietary field that describes the VLAN ID in which the BPDU was originated. Not quite sure how this may have happened because PVST and RPVST BPDUs should always carry this field, and IEEE STP/RSTP BPDUs that do not have it would never get encapsulated, addressed and processed like PVST/RPVST BPDUs. Still, checking for native VLAN mismatches or inadvertent inter-VLAN interconnections is the first thing to do in these cases.
I veried config and outputs on both sides affected ports. Configuration of trunks seems to be ok. Firts port of Nexus is directly connected to other N7k and second interface (sorry, this log messages was discovered on two interfacess) is connected to Cat 65k.
I will check inter-Vlan interconnections. I separately opened TAC, but I'm very interested in this problem by reason of the other case.
It is possible that the offending BPDU was generated by a faulty IOS and that there is nothing wrong either with your configuration or with your physical cabling. Still, checking for configuration mistakes, native VLAN mismatches and inadvertent interconnection of ports in different VLANs is the first step in solving this issue, and I expect the TAC to request the same.
I did not quite understand your topology description. Do you believe you could upload an exact topology diagram depicting the interconnected switches and their links?
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...