EDIT: After a reboot of the server everything is running fine again.
last night we did an upgrade of our UCS to 4.3-1 errata126. Unfortunately something seem to went wrong. We encountered problems by connecting to virutal machines and recognized that they are not able to receive an IP adress from the DHCP service. Providing a fixed IP to the virtual machines helps to provide their services. Due to some reason the DHCP client list ist also empty. in the log /var/log/daemon.log I found following error very often
virtlogd: 2018-06-28 09:50:30.819+0000: 3116: error : virNetSocketReadWire:1801 : End of file while reading data: Eingabe-/Ausgabefehler
Any ideas what that could be?