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Settting up network in KVM

When installing a KVM VM in Ubuntu, one of the question is: How to configure its network.
There is basically two choices:
  • A virtual bridge that will NAT the VMs connected to it.
  • A physical bridge so that all VMs will be able to have a "public" IP address

NATing virtual bridge (default, virbr0)

This is the default bridge if you follow the Ubuntu Official tutorial.
This bridge will act as a DHCP server + a gateway. VMs will be able to reach internet but their source IP address will be seen as the virbr0 IP.

Non-NATing bridge

Most of my time, I want to use VMs as public servers. Having them NATed as described above is quite uselss for that purpose.
Libvirt allows to do that, assuming you have
The steps:
  • Create a bridge containing only the physical existing interface
  • Each created VM will then join that bridge
Creating a VM that way is described on a precedent blog post.

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