Centralized Routing on Single Rack Small Data Center Leaf Pair (not Border Leaf Pair)

The following items are required before you configure centralized routing on Single Rack Small Data Center Leaf Pair.

The device-role (leaf or border-leaf) are specified during the addition of the devices to the fabric, prior to the “fabric configure”.
Border-Leaf pair can exist in a Clos or Small Data Center fabric irrespective of the VRFs instantiated in the fabric are distributed or centralized.
Device role border-leaf implies the leaf pair used at the edge (border) of the fabric, and not restricted to the centralized routing.
Tenant (PO, VRF, EPG, or BGP) provisioning happens on a configured fabric.
Only the Border-Leaf devices can act as Centralized Routers.
Default routing-type for a VRF is “distributed” and you need to explicitly provide the value “centralized” if needed.
During the creation of the VRF as a CR (Centralized Router), EFA needs to instantiate the VRF on a pair of Border-Leaf devices.
If the fabric (Clos or Small Data Center) has only one pair of Border-Leaf devices then the same pair is chosen as the designated CRs (Centralized Routers) for the VRF. Else, need to explicitly provide the Border-Leaf devices as the designated CRs (Centralized Routers) during the creation of the VRF.
EFA is designed to expand or compress with the addition or deletion of racks (rack = MCT-pair) as per your requirement.
EFA cannot determine “a given fabric is a single rack small data center fabric and can never be expanded beyond that”. Hence there is no specific automation for a single-rack use case.
For CR on a single rack small data center fabric, EFA recommends that you configure the fabric with the device-role = border-leaf for both the MCT nodes.
If you want to use Day 1 Centralized Routing provisioning on a “Day 0 Configured Single Rack Leaf Small Data Center Fabric”, then the same results in failure because CR can be instantiated only on the border-leaf pair of the small data center fabric.
You cannot recreate the fabric with device-role = border-leaf.

Fabric Setting for a single-rack-deployment

A new fabric setting “single-rack-deployment” is introduced as follows:
```
efa fabric setting update --name <non-clos-fabric-name> --single-rack-deployment <Yes|No>
```
The fabric setting is applicable only for the Small Data Center fabric.
Default value of single-rack-delployment = No.
After upgrade from EFA 2.4.x to EFA 2.5.0, all the EFA 2.4.x small data center fabrics have single-rack-deployment =No.
Single Rack Deployment
1. When the “single-rack-deployment = Yes” and the fabric is configured,
  - You are not allowed to modify the single-rack-deployment from Yes to No.
  - The state is used as an indicator to EFA that “a given fabric is a single rack non clos fabric and will never be expanded beyond that”, so that EFA can have specific automation for the specific scenario of allowing the non-border-leaf rack act as CR (Centralized Router) for single rack small data center leaf pair deployments.
  - You cannot expand such a fabric. If you intend to expand such a fabric, then you must delete the fabric and recreate the same with “single-rack-deployment = No”.
2. When the “single-rack-deployment = Yes” and the fabric is not configured,
  - You can modify the single-rack-deployment value from Yes to No.
Multi Rack Deployment
1. When the “single-rack-deployment = No” and fabric is configured or not-configured,
  - You can modify the value of single-rack-deployment from No to Yes, provided the existing number of racks in the fabric is 1.
Fabric Device Add
- Validations are done to ensure the number of racks in the given fabric adhere to the fabric settings.