_c2c_overlay.html.md.erb

## <a id="overlay"></a> Configure the Overlay Network

Container-to-container networking uses an overlay network to manage communication between app instances. By default, each Diego Cell in the overlay network is allocated a /24 range that supports 254 containers per Diego Cell, one container for each of the usable IP addresses, `.1` through `.254`. For more information about the overlay network, see [Overlay Network](../../concepts/understand-cf-networking.html#overlay-network) in _Container-to-Container Networking_.

### <a id="cells"></a> Configure the Number of Diego Cells

To modify the number of Diego Cells supported by the overlay network:

1. Navigate to the <%= vars.ops_manager %> Installation Dashboard.

1. Click the <%= vars.app_runtime_abbr %> tile.

1. Select **Networking**.

1. Under **Overlay subnet**, enter an IP range for the overlay network. By default, <%= vars.ops_manager %> uses `10.255.0.0/16`. Modifying the subnet range allocated to the overlay network changes the number of Diego Cells supported in your deployment.

    <table>
      <tr>
        <th>Overlay subnet mask</th>
        <th>Number of Diego Cells</th>
        <th>Containers per Diego Cell </th>
      </tr>
      <tr>
        <td>/20</td>
        <td>15</td>
        <td>254</td>
      </tr>
      <tr>
        <td>/16</td>
        <td>255</td>
        <td>254</td>
      </tr>
      <tr>
        <td>/12</td>
        <td>4,095</td>
        <td>254</td>
      </tr>
    </table>
    <p class="note warning"><strong>Warning:</strong> The overlay network IP address range must not conflict with any other IP addresses in the network. If a conflict exists, Diego Cells cannot reach any endpoint that has a conflicting IP address.</p>