Table of Contents
No network communication via vhost interface
Error description
Suddenly network communication via the management interface of the KVM host is not possible. The command ifconfig displays an active ethernet interface but no outgoing network packages. The switch port to which the network interface is connected is shown as active. Disconnecting and reconnecting the network cable between switch port and ethernet port does not solve the problem. Firewall restrictions (e.g. by iptables) are not configured. No firewall rules are configured inside libvirt (e.g. by virsh).
Failure cause
The failure cause is completely unknown. It was never observed before that one of two network interfaces with identical hardware configurations fails like observed while the other one still works.
Solution
The problem could only be solved by live migration of all vhosts running on the affected KVM host to other KVM hosts, rebooting the KVM server and migrating the vhosts back to the affected KVM host. After reboot the affected network interface was working as before the appearance of the error.