# Changes in Release 0.3

## Selecting a virtualization provider

Release 0.3 added support for multiple virtualization providers. The provider is specified in the **provider** top-level element in the topology file, or as **defaults.provider** element. The default provider (specified in system-level `topology-defaults.yml`) is *libvirt*.

You'll find the up-to-date status of virtualization provider support in [Supported Platforms](../platforms.md)

## Explicit device images

In release 0.2, the default device images (Vagrant boxes) were hard-coded in device part of Vagrantfile templates. 

```{warning}
The rest of this section no longer applies. Release 1.1.3 changed the image settings, see [defaults](../defaults.md) page for details
```

Those defaults are gone, the default device image is specified in **defaults.devices._device_.image._provider_**.

You can override the defaults by specifying topology defaults. To change the default Vagrant box for CSR 1000v in *libvirt* environment use:

```
defaults:
  devices:
    csr1000v:
      image:
        libvirt: cisco/csr1000v-16.7
```

You can also specify device-specific image with the *image* or *box* parameter in node data.

## Provider Defaults

**providers** element was added to the **defaults** data structure. It's a dictionary listing all valid providers. The absolute minimum you have to specify for a provider is the name of the configuration file (in the **config** element), for example:

```
providers:
  libvirt:
    config: Vagrantfile
  virtualbox:
    config: Vagrantfile
```

## Ports Defaults

Topology defaults also contain a **ports** dictionary mapping protocols (SSH, HTTP, NETCONF) to TCP port numbers. Call me lazy: it was simpler to add a dictionary than to deal with `/etc/protocols`.

```
ports:
  ssh: 22
  http: 80
  https: 443
  netconf: 830
```

Protocol names must match names of forwarded ports in **providers._provider_.forwarded** dictionary.

**WARNING:** These data structures are not checked. If you're messing with them you better know what you're doing.