how to connect kvm virtual machines directly to external IP's

Question

I know this question was asked here and there but no answer works for me. After hours of googling I can't figure it out. I have Ubuntu 14 server and I need to make few virtual servers - I want something like VPS in DigitalOcean - Virtual machines with external IP.

So I have an Ubuntu server with couple IPs but only one physical network card.

The host system must be accessible only by the main address 198.201.29.211.

Of course virtual machines should behave like normal physical servers and be also able to connect to host server.

This is my /etc/networking/interfaces file:

# Loopback device:
auto lo
iface lo inet loopback
iface lo inet6 loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   198.201.29.211
  netmask   255.255.255.192
  gateway   198.201.29.193
  # default route to access subnet
  up route add -net 198.201.29.192 netmask 255.255.255.192 gw 198.201.29.193 eth0

auto eth0:0
iface eth0:0 inet static
  address 198.201.29.247
  netmask 255.255.255.192

auto eth0:1
iface eth0:0 inet static
  address 198.201.29.248
  netmask 255.255.255.192

auto eth0:2
iface eth0:0 inet static
  address 198.201.29.249
  netmask 255.255.255.192

Every IP (except the main one: 198.201.29.211 on eth0) should be exclusively attached to appropriate virtual machine (inside on eth0).

The IP addresses must be configured in the guests, not in the host! — Michael Hampton, Apr 01 '16 at 19:20
OK - I understand I should remove all eth0:0, eth0:1 etc, yes? — Kornel, Apr 01 '16 at 19:21
But what about br0 or routing? I was trying br0 but without success. How br0 should look like? — Kornel, Apr 01 '16 at 19:23

score 1 · Answer 1 · edited Apr 13 '17 at 12:14

It turned out that the correct configuration is pretty simple. (There is so many confusing answers over the internet). The Network source setting (I use virt-manager) should be set to Host device eth0 (Bridge 'br0').

The address for the virtual machine needs to be set up ONLY in virtual machine what uses it and NOT on the host.

The virtual machine /etc/networking/interfaces looks like this:

auto  eth0
    iface eth0 inet static
      address   198.201.29.248
      netmask   255.255.255.192
      gateway   198.201.29.211

And this is my working /etc/networking/interfaces (on host machine):

# Loopback device:
auto lo
iface lo inet loopback
iface lo inet6 loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   198.201.29.211
  netmask   255.255.255.192
  gateway   198.201.29.193
  # default route to access subnet
  up route add -net 198.201.29.192 netmask 255.255.255.192 gw 198.201.29.193 eth0

auto br0
iface br0 inet static
  address   198.201.29.211
  netmask   255.255.255.192
  gateway   198.201.29.193
  bridge_ports eth0
  bridge_stp off
  bridge_fd 0
  bridge_maxwait 0

Thaks to this post: KVM/Libvirt bridged/routed networking not working on newer guest kernels I have found out that because my server is in Hertzner i also have to switch off ICMP redirections:

for file in `find /proc/ -iname send_redirects`; do echo 0 > $file; done

how to connect kvm virtual machines directly to external IP's

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