In addition to the patrick's post i would suggest to check this out which clearly talks about the network problems created by a newly inducted switch..
"How a Recently Inserted Switch Can Cause Network Problems"
This problem occurs when you have a large switched domain that is all in the same VTP domain, and you want to add one switch in the network.
This switch was previously used in the lab, and a good VTP domain name was entered. It was configured as a VTP client and was connected to the rest of the network. Then, the ISL link was brought up to the rest of the network. In just a few seconds, the whole network is down. What could have happened?
The configuration revision of the switch you inserted was higher than the configuration revision of the VTP domain. Therefore, your recently-introduced switch, with almost no configured VLANs, has erased all VLANs through the VTP domain.
This happens whether the switch is a VTP client or a VTP server. A VTP client can erase VLAN information on a VTP server. You can tell that this has happened when many of the ports in your network go into inactive state but continue to be assigned to a nonexistent VLAN.
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 customers befor...
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