Kubernetes requires that packets traversing a network bridge are processed for filtering and for port forwarding. To achieve this, tunable parameters in the kernel bridge module are automatically set when the kubeadm package is installed and a sysctl file is created at /etc/sysctl.d/k8s.conf that contains the following lines:

net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1

If you modify this file, or create anything similar yourself, run the following command to load the bridge tunable parameters:

$ sudo /sbin/sysctl -p /etc/sysctl.d/k8s.conf