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Create a Brownfield Deployment to Add an Overlay to an Existing IP Fabric


When you add an overlay onto an existing data center network (sometimes called a brownfield deployment), you need to make sure the IP fabric is fully in place.

We are adding an overlay to a centrally-routed bridging (CRB) fabric as shown in figure Figure 1.

Figure 1: Centrally-Routed Bridging IP Fabric
Centrally-Routed Bridging
IP Fabric

Once the underlay is in place, Contrail Command does the following to add the overlay:

  • Discovery of the underlay (devices, interfaces, and management network)

  • BGP configuration and EVPN-VXLAN baselined for the overlay based on configured device roles.

Before You Begin

The brownfield overlay procedure assumes that the following are established before you provision the overlay.

  • Management network

  • Hostname and router ID

  • Remote access to fabric devices using SSH or NETCONF

  • IP addresses configured on all the fabric interfaces

  • Physical interfaces with LLDP between fabric devices and an MTU of at least 2000

  • Loopback interfaces with IP addresses

  • Underlay routing protocols

    For the most successful results, we recommend that you use EBGP for the underlay and configure it as follows:

    • Configure each spine and leaf device with its own AS number

    • EBGP peering between all fabric devices (using local-as)

    • EBGP policy to advertise BGP and direct and connected routes

      It is considered good practice to tag routes with a community based on local EBGP AS number

  • Routing information base (RIB) and forwarding information base (FIB) multipath with per-packet load balancing and fast reroute functionality enabled.

For more information about configuring an IP fabric, see IP Fabric Underlay Network Design and Implementation in the Data Center Fabric Architecture Guide.

Adding an Existing Underlay into a Fabric and Discovering Devices

  1. Open a web browser, navigate to the Contrail Command URL, enter your user name and password, and click Log in.

    The format for the Contrail Command URL is https://contrail-command-server-ip-address:9091. 9091 is the port that gives you access to Contrail Command.

    Contrail Command displays a status dashboard as the home page.

  2. Navigate to Infrastructure > Fabrics and click Create.

    The provision option box appears.

  3. Select Existing Fabric as the provisioning option and click Provision.

    The Create Fabric screen displays.

  4. Fill in the following fields.



    Value Used in This Example


    Name of your fabric


    Overlay ASN (IBGP)

    AS number for the EVPN overlay (Default is 64512)


    Node Profiles

    Device types that are available in your fabric

    Default, which selects all device types

    VLAN-ID Fabric-Wide Significance

    Select the VLAN-ID Fabric Wide Significance check box to enable enterprise style of configuration. In this mode, Contrail Networking ensures that every Layer 2 Service or VLAN ID in a fabric is unique, and that there is a 1:1 mapping between the VLAN ID (4K VLANs per fabric) and the Virtual Extensible LAN Network Identifier (VNI).

    In most cases, 4K bridge domains are more than enough for any enterprise deployment. Fabric-wide significance of a VLAN ID implies that any VLAN being provisioned in an EVPN VXLAN fabric maps to a VNI in a 1:1 ratio.

    Box is checked

    Device credentials

    Username and root password of your fabric devices.

    Username: lab

    Password: ******

    Management subnets

    CIDR: IP address and prefix of the management subnet


    Loopback Subnets

    CIDR: IP address and prefix of the loopback subnets.

    This is a mandatory field, if your underlying network does not have loopback addresses configured.


  5. Click Next, and the Device Discovery process begins.
  6. When the Device Discovery process is complete, click Next.

Assigning Device Roles

After the new fabric devices have been discovered, the Assign the roles screen displays. You must assign the roles that the devices will perform in the fabric.

To assign fabric device roles:

  1. Put a check in the box next to the device or devices for which you want to assign roles. To save time, check the boxes for more than one device to assign the same role to multiple devices at once.
  2. Next to the spine devices, select Assign Roles.
  3. Add the following roles to the spine devices and click Assign.
  4. Add the following roles to the leaf devices and click Assign.

    See Device Roles for information about configuring roles.

Applying the Role-Based Configurations to Fabric Devices

After you have assigned roles to the fabric devices, use Autoconfigure to generate role-based configurations and push them to the devices. To do so:

  1. When you are done assigning roles, click Autoconfigure.
  2. Track the progress of the Autoconfiguration process.
  3. When the autoconfiguration is complete click Finish.

    On the resulting screen, you can view the completed status of the fabric.

Verifying Your Fabric

To verify BGP peering among the spine and leaf devices, enter the following command in the Junos OS CLI on Spine 1. You should see that the other spine device and the leaf devices are all BGP peers.

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