[one-users] Libvirt with NAT

[Shankhadeep Shome]

Yes, you need to create a regular bridge device and attach it to a tap
device, you can use virt-manager to create this for you, the tap device
will be disabled. You will also need an iptables rule to nat packets
to/from the bridge, again the virt-manager can do this for you.

[vnics] -- [bridge] -- [disabled tap]

Here is a bridge definition for infiniband devices that cannot use mac
bridges, created by virt-manager

Its creating a 172.16.100.128/25 network, note. do not configure a dhcp
server if you want opennebula to track your IPs, all you need to do is give
open nebula the iprange 172.16.100.130-254 to manage and configure your
contextualization appropriately.

<network>
  <name>ibnat0</name>
  <uuid>4d7e9211-3a32-8b77-90a6-3b45c8d98ddb</uuid>
  <bridge name='virbr1' stp='on' delay='0' />
  <mac address='52:54:00:8B:34:92'/>
  <ip address='172.16.100.129' netmask='255.255.255.128'>
  </ip>
</network>

ifconfig -a output, this is what it looks like

ib0       Link encap:UNSPEC  HWaddr
80-00-00-48-FE-80-00-00-00-00-00-00-00-00-00-00
          inet addr:192.168.10.10  Bcast:192.168.10.255  Mask:255.255.255.0
          inet6 addr: fe80::208:f104:39a:63b1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:65520  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:5 overruns:0 carrier:0
          collisions:0 txqueuelen:256
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

virbr1    Link encap:Ethernet  HWaddr 52:54:00:8b:34:92
          inet addr:172.16.100.129  Bcast:172.16.100.255
 Mask:255.255.255.128
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

virbr1-nic Link encap:Ethernet  HWaddr 52:54:00:8b:34:92
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

The nat rule will be something like this..

*iptables -t nat -A POSTROUTING -s 172.16.100.128/25 -o eth0 -j SNAT
--to-source 192.168.10.10*

iptables -v -L -t nat (And here is the output of that rule)
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source
destination

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source
destination

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source
destination

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source
destination
    0     0 SNAT       all  --  any    eth0    172.16.100.128/25
 anywhere             to:192.168.10.10


On Wed, Jul 25, 2012 at 6:24 AM, Javier Alvarez <javier.alvarez at bsc.es>wrote:

>  Hello,
>
> I would like to know if OpenNebula supports the use of NAT forwarding as
> explained in the networking page of the libvirt's wiki:
>
>
> http://wiki.libvirt.org/page/Networking#NAT_forwarding_.28aka_.22virtual_networks.22.29
>
> Thanks,
>
> Javi
>
> --
> Javier Álvarez Cid-Fuentes
> Grid Computing and Clusters Group
> Barcelona Supercomputing Center (BSC-CNS)
> Tel. (+34) 93 413 72 46
>
>
>
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