How to configure networking with a /29 subnet?


Can you please spare some suggestions here as I am clueless. I am new with Cloudmin.

I have just rented a server from Hetzner with 1 IP (as per server default) plus a /29 subnet.
I installed cloudmin without any issues (Centos 5.8 64bit).
I have put the IPs pool inside cloudmin and I created a couple of VMs inside from stock images.
The problem is that netwoking does not work. My main host has no issues whatsoever however I cannot see the VMs. The VMs cannot ping outside (when checked via Graphical Java console).

Can you point me where to look?

I understand that I can choose between routing and bridging. What I would like to have is totally independent and isolated VMs that have their own software firewall since each VM will have different firewall rules.

Any help is much appreciated!

Thank you


This sounds like a routing issue - you may have to configure your Xen VMs to use your host system as a router, and enable routing on the host.

You can change the default route on a VM by shutting it down, then going to System Configuration -> Network Interfaces -> Default gateway options.

You can enable routing on the host at Webmin -> Networking -> Network Configuration -> Routing and Gateways -> Act as router.

Thr saga continues…

After clarifying that Cloudmin for KVM is compatible with Centos 6.3 I have decided to go for it thinking that network settings might be easier to configure in Cloudmin.
( link )

However… after installing Cloudmin for KVN and rebooted, the system became inaccessible (DataCenter hosting) and after a few moments I realized that this was because the installer had installed a bridge which was not allowing me to access it (no ping no nothing).

Can someone please with decent knowledge of Linux networking help me to configure the KVM network installation properly so I can move on???

I can always make manual changes to the network scripts before the last reboot (following Cloudmin installation).


I have a similar howto for Ubuntu however I don’t know how to do it in Centos or Webmin.

H-E-L-P !!!

The bridge interface is definitely needed for KVM virtual machines to work. However, the Cloudmin installer should setup the bridge with the same IP address that you had on eth0, so that networking to the host continues to work.

What is the current state of your system? Is networking completely offline?

After the reboot I cannot access the server remotely.
I asked the DC to connect me a virtualKVM and I realised tha the server was starting normaly however with no Internet access. I could not even ping the gateway.
The eth0 has no IP address and the br0 has the following settings:


y.y.y.y is the main server IP
x.x.x.x is the gateway as given from the DC

Any ideas?

Could you post the output from the following commands :

ifconfig -a netstat -rn

why don’t publish a tutorial to setup via command line and/or Webmin features, to help all the users of Hetzner ???
Thank You

I personally cannot because I am not using Cloudmin.

You have discontuned your Cloudmin environment ??
I have forgot to write that the invitation is for the developers of Cloudmin…

Since there are several users on Hetzner who run into this issue, I’ll be working on a doc for KVM and routed networking over the next day or two. I’ll update this thread when it is done…

Very well Jamie ! Thank You in advance, I suggest to open a section into the documentation, a sort of wiki…“Routed Network Setup for Kvm Hosts”

It could be possible to add into the Networking Section of Webmin the possible Network scenario, giving to the user the fields to write the ip and let to Webmin to manage the settings for the eth0, br0 and all the other required settings to the etc/sysconfig/network-scripts/… ??

Also will be nice to have a bonding setup for 2 Uplink or to manage 2 or more Uplink for the further possible purposes.

For the “press” I notice you that I have just followed the guide publishe in on hetzner wiki
and of course did the settings but Vps is still offline !

After the network restart I had no errors, but the Vm wasn’t online, I thought to modify the gateway, in the networking, for the br0 with the main ip of the server, as the gateway for the additional subnet is the main ip assigned to the server…but I was wrong and now I have the server offline…waiting for the kvm to look into what I did and fix it…I hope…:slight_smile:

Bye Bye

All is up and running, the Cloudmin Experiment is started !

Although I am not using Cloudmin anymore (due to the minimal support of the DC and the forums here) I would like to see the network how-to configuration on a Cloudmin server with a /29 subnet. Please update this thread when this is done.

I’ve created a new doc on configuring a network bridge, as used at Hetzner. You can find it at

Please let me know how it goes…

Better late than never. Many thanks for the how-to.
I do have two questions though:

  1. Is it possible to have two bridges, one with a public IP (from the subnet) and one with an internal such as the you are describing in the how-to?

I currently use Proxmox but I would like to create a server with Cloudmin. Before I do that however I need to know that it will work otherwise I am wasting money on the DC.
In my current Proxmox setup I have one bridge with takes one of the subnet IPs. The KVMs created use on of the remaining IPs as their IPs and that bridge as a gateway, which makes this handy, however I am “wasting” one very valuable IP.
I would like therefore to know if (with Cloudmin) I will be able to have that setup PLUS add another bridge with say address that will act as a gateway to other KVMs. The reason behind that is because Hetzner will not assign additional IPs (singles or ranges) to me anymore, and hence I need to use the IPs for multiple internal hosts.
Of course we are talking about two-way internet access to all KVMs.
Is this possible, and if yes, will one NIC card be enough?
Can you post that type of How-to as well please?

  1. In your how-to what is required to add in order to have 2-way internet?

We are surely getting somewhere!

Yes, you could do that - you’d have to repeat the bridge setup process twice to create br1 and br2, one using real IPs and one using internal IPs. On the virtual system creation page there should be a field to select which bridge to use…