Hetzner is a hosting company in Germany where you can rent dedicated root servers per month. Using their KVM-over-IP setup, it is possible to install operating systems that are not available by default, such as XenServer by Citrix. With the machine, you get four public IP addresses. One of these addresses is given to you when the machine is assigned to you, the other three are assigned to you on request.
There is a problem with the public IP addresses Hetzner gives you. Within the Hetzner network, there is a hard connection between the MAC address of your machine and the IP addresses you have been given. This is a problem for virtual machines that are bridged onto the network by the host machine. These virtual machines have their own MAC address and the Hetzner network will drop packets from these unknown MAC addresses.
There is a solution to this problem: have the host machine route IP packets from the virtual machines to the network and vice versa. We will use the following addresses in the example below:
| IP addresses | 188.40.109.204 (host), 188.40.109.250 (VM) |
| Netmask | 255.255.255.192 |
| Gateway | 188.40.109.193 (host) |
| DNS | 213.133.100.100 |
We start with the configuration of the host machine (running XenServer). The first file is the configuration file of eth0: /etc/sysconfig/network-scripts/ifcfg-eth0
XEMANAGED=yes DEVICE=eth0 ONBOOT=no TYPE=Ethernet HWADDR=40:61:86:be:ce:88 (replace with MAC address of host) BRIDGE=xenbr0
Notice that this file does not contain any IP configuration. The second file is the configuration file of xenbr0: /etc/sysconfig/network-scripts/ifcfg-xenbr0
XEMANAGED=yes DEVICE=xenbr0 ONBOOT=no TYPE=Bridge DELAY=0 STP=off PIFDEV=eth0 BOOTPROTO=none IPADDR=188.40.109.204 (replace with IP address of host) NETMASK=255.255.255.192 GATEWAY=188.40.109.193 (replace with gateway of host) DNS1=213.133.100.100 DNS2=213.133.99.99 DNS3=213.133.98.98
Now we need to enable IP forwarding on the host machine. We start with the sysctl configuration file: /etc/sysctl.conf
net.ipv4.ip_forward=1 net.ipv4.conf.all.send_redirects=0 net.ipv4.conf.default.send_redirects=0 net.ipv4.conf.lo.send_redirects=0 net.ipv4.conf.xenbr0.send_redirects=0
The first line tells the machine to perform IP forwarding. The four lines after that tell the machine to disable sending ICMP redirects. The last file we need to edit is the firewall configuration file: /etc/sysconfig/iptables. Add this text below the line -A RH-Firewall-1-INPUT -i lo -j ACCEPT:
-A RH-Firewall-1-INPUT -i xenbr0 -o xenbr0 -j ACCEPT
Now reboot the machine and continue with the IP configuration of the virtual machine running on XenServer. There is only one file we need to edit here, which is the configuration file of eth0: /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0 BOOTPROTO=none ONBOOT=yes HWADDR=8e:35:1e:3b:12:aa (replace with MAC address of VM) IPADDR=188.40.109.250 (replace with IP address of VM) NETMASK=255.255.255.192 GATEWAY=188.40.109.204 (replace with IP address of host)
The gateway in this configuration is crucial: it needs to be the IP address of the host itself, not the gateway of the host.
thank you for this tutorial, but what do you do if there are several VMs (and several IP addresses)
The main part of the tutorial stays the same. Just repeat the bottom part where we configure the VM, using a different IP address for each VM.
Thank you, Jan for quick reply. I tried so, but when I started dummy interface I got this:
ifup xenbr0:1
Device xenbr0:1 has different MAC address than expected, ignoring.
maybe it’s expecting mac from eth0 .. and still no ping to vm
sorry, ping is ok, but vm is throwing error about ip conflict
vm network configuration is the same as xenbr1:0
what if vm and host ip are in different subnets ?
I haven’t tested it yet, but it probably means that you need to assign the host one of the IP addresses in the extra subnet and then use that IP address as the gateway for the VM.
I would also like to add another network (192.168.x.x). No problem to install it on the VMs, but how do I configure the Host so I get internet access from a VM using such a private IP only?
[...] IP addresses up to /24 with 254 IP addresses). Due to the MAC filters in the Hetzner firewalls (see “Using XenServer in a routed IP network”), traffic from the virtual machines need to be routed by the host system. To enable this routing, I [...]
Thank you very much! It solved my problem!
This has been a very helpful guide for 5.6!! Thanks a lot! -But things has changed for 6.0 Is there any chance some knows how to tackle that one..?