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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 FabricCentrally-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.

  2. Navigate to Infrastructure > Fabrics and click Create.

    The provision option box appears.

  3. Select Existing Fabric and click Provision.

    The Create Fabric screen displays.

  4. Fill in the following fields.


    Value Used in This Example



    Overlay ASN (IBGP)


    Node Profiles

    Default, which selects all device types

    Disable VLAN-VN Uniqueness Check

    Box is unchecked

    VLAN-ID Fabric-Wide Significance

    Box is checked

    Device credentials

    Username: lab

    Password: ******

    Management subnets


    Loopback Subnets


  5. Click Next, and the Device Discovery process begins.
  6. After the new fabric devices are discovered, the Assign the roles screen displays. You need to assign the roles that the devices will perform in the fabric.

  7. 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.
  8. Next to the spine devices, select Assign Roles.
  9. Add the following roles to the spine devices and click Assign.
  10. Assign the CRB-Access role to the leaf devices and click Assign.

    See Device Roles for information about configuring roles.

  11. When you are done assigning roles, click Autoconfigure to generate role-based configurations.
  12. When the autoconfiguration is complete click Finish.

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