Proxmox - Networking - Routed Networking

To hide VMs behind the host IP use a routed networking configuration.

Create another virtual network interface and enable routing on this interface. 

vi /etc/network/interfaces

Modify the eth0 interface:

/etc/network/interfaces
auto eth0
iface eth0 inet static
        post-up echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp

NOTE: A routed configuration needs proxy arp to be enabled on the outgoing interface.

Create the virtual interface and enable routing by adding those lines:

/etc/network/interface
auto vmbr1
iface vmbr1 inet static
        address 10.3.5.1
        netmask 255.255.255.0
        bridge_ports none
        bridge_stp off
        bridge_fd 0
        post-up echo 1 > /proc/sys/net/ipv4/ip_forward

NOTE: The last line will enable routing on the interface.

  • With this configuration the VM traffic will routed using the routing table of the host.
  • The outside world needs to know, how to reach the 10.3.5.0/24 subnet.

Using NAT

To avoid working with static routes, NAT the traffic:

/etc/network/interfaces
        post-up iptables -t nat -A POSTROUTING -s '10.3.5.0/24' -o eth0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '10.3.5.0/24' -o eth0 -j MASQUERADE

NOTE: This will enable the NAT function for the internal network 10.3.5.0/24 by using eth0 as the egress network.