Proxmox Routed Networking

When using Proxmox on the F2H network there are some special networking requirements that need to be configured inside your server. Without this special configuration, Proxmox guests will not be able to communicate with the outside world. This guide details a Proxmox routed networking configuration. This means you cannot use single IPs (/32 subnets) but you can use other subnet types.

Allow IP Forwarding

In all of our OS distributions, we disable IP forwarding as standard. Because our bridge will not be connected physically to the ethernet adapter we need to enable forwarding for IPv4 and IPv6. This is done in the /etc/sysctl.conf file or by issuing the following commands.

sysctl -w net.ipv4.ip_forward=1
sysctl -w net.ipv6.conf.all.forwarding=1

You may need to remove the comment (#) from the lines in the /etc/sysctl.conf file. In some distributions, there are no comments. Ensure the file looks like the image below. Reboot the host after making these changes.

Proxmox Interfaces Configuration

The interfaces file contains all of the required networking settings. Here we create a bridge and add any additional IPs. Do not create the bridge in the Proxmox GUI. When we make the changes in the interfaces file, these will be replicated to the GUI. We have also provided a copy of this file located here with comments and further information.

 auto lo
 iface lo inet loopback
 iface lo inet6 loopback
 auto enp5s0
 iface enp5s0 inet static
         address 176.xx.xx.36/27
         gateway 176.xx.xx.33
       # pointopoint GATEWAY-IP
         broadcast 176.9.24.63
         up route add -net 176.x.xx.32 netmask 255.255.255.224 gw 176.x.xx.33 dev enp5s0

 iface enp5s0 inet6 static
         address 2a01:4f8:150:2218::2/64
         gateway fe80::1

 auto vmbr0
 iface vmbr0 inet static
         address 176.x.xx.36/27
         broadcast 176.x.xx.63         bridge-ports none              bridge-stp off         bridge-fd 0
         bidge_maxwait 0     
up route add -host 178.63.xxx.225 dev vmbr0     up route add -host 178.63.xxx.224 dev vmbr0     up route add -host 178.63.xx.226 dev vmbr0    up route add -host 178.63.xxx.227 dev vmbr0    up route add -host 178.63.xxx.228 dev vmbr0     up route add -host 178.63.xxx.229 dev vmbr0     up route add -host 178.63.xx.230 dev vmbr0     up route add -host 178.63.xxx.231 dev vmbr0     
 auto vmbr1
 iface vmbr1 inet static
         address  10.10.10.1
         netmask  255.255.255.0
         bridge_ports none
         bridge_stp off
         bridge_fd 0
 post-up echo 1 > /proc/sys/net/ipv4/ip_forward     
post-up iptables -t nat -A POSTROUTING -s '10.10.10.0/24' -o vmbr0 -j MASQUERADE     post-down iptables -t nat -D POSTROUTING -s '10.10.10.0/24' -o vmbr0 -j MASQUERADE

After making the required changes reboot the host. So, in the Proxmox GUI, you should now see your adapter and bridge. Check the network page. If you see the new adapter and bridge you can now continue to create a guest VM or container.