We have proxmox 3.1 server in netzner with routuing network and IP subnet block. We want to implement csf firewall without interfering the traffic of the KVM VMs, what would be the easiest way? We readed that we should add this lines to /etc/csf/csfpost.sh: iptables -A FORWARD -d 144.76.223.155 -j ACCEPT iptables -A FORWARD -d 144.76.223.156 -j ACCEPT iptables -A FORWARD -d 144.76.223.157 -j ACCEPT iptables -A FORWARD -d 144.76.223.158 -j ACCEPT iptables -A FORWARD -d 144.76.223.159 -j ACCEPT iptables -A FORWARD -d 144.99.183.323 -j ACCEPT But when we enable csf the ping breaks, this is the network config (IPs are modified): auto lo iface lo inet loopback # device: eth0 auto eth0 iface eth0 inet static address 144.76.166.100 netmask 255.255.255.255 pointopoint 144.76.183.97 gateway 144.76.183.97 # for single IPs auto vmbr0 iface vmbr0 inet static address 144.76.166.100 netmask 255.255.255.255 bridge_ports none bridge_stp off bridge_fd 0 up ip route add 144.99.183.323/32 dev vmbr0 # for a subnet auto vmbr1 iface vmbr1 inet static address 144.76.166.100 netmask 255.255.255.248 bridge_ports none bridge_stp off bridge_fd 0 Thanks in advanced ! :)