DNA Center or the devbox is not able to reach any network devices, the switches may be down or have a wrong IP etc [root@devbox ~]# arp -na? (10.10.20.254) at 00:00:0c:9f:f0:0b [ether] on ens192? (10.10.20.84) at <incomplete> on ens192? (10.10.20.251...