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General Information

IP block we want to use on server B: 171.32.42.128/29 Internal IP Block used for communication: 10.0.0.0/30 Bridge interface server B: br0

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Server B

  1. Setup the GRE tunnel on server B.
ip tunnel add gre1 mode gre local <IP server B> remote <IP server A> ttl 255
ip addr add 10.0.0.2/30 dev gre1
ip link set gre1 up
  1. Enable IP forwarding. [only execute once]
sudo modprobe ip_gre
lsmod | grep gre
sudo apt install iptables iproute2
sudo echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf
sudo sysctl -p
  1. Route data from the GRE tunnel to the bridge and back.
ip route add default dev gre1 table 3
ip rule add from 171.32.42.128/29 table 3
ip route add 171.32.42.128/29 dev br0 table 3
ip addr add 171.32.42.128/29 dev br0 (If not already added to the bridge via netplan config)
You should be able to ping server A from server B. 
Ping Server A
ping 10.0.0.1
To configure netplan, save configuration files under /etc/netplan/ with a .yaml extension (e.g. /etc/netplan/config.yaml), then run sudo netplan apply. This command parses and applies the configuration to the system. Configuration written to disk under /etc/netplan/ will persist between reboots. Example file contents : /etc/netplan/01-netcfg.yaml Note: You will need the bridge-utils package installed on your server
  1. Add the following lines to the netplan file on the same level as “ethernets”
bridges:
  br0:
    addresses: ["171.32.42.129/29"]
Use the following network config in the adapter of your VM: 
IP address: 191.80.60.130
Mask: 255.255.255.248 (depends on the subnet)
Gateway: 171.32.42.129
We recommend setting the MTU of the bridge / VM network interface to 1476 as otherwise packet fragmentation may occur.
That’s it! Configure the network bridge and IPs in Virtfusion. On a server restart all the things we did will be wiped out. To make sure the GRE tunnel and everything else is going to work after a restart we have to edit the file /etc/rc.local and add all the commands we did (except for the echo ones!) before the exit 0.