SD-Access Fabric Operation

SD-Access Fabric Operation

SD-Access Fabric Operation

In this Module we will discuss about Fabric Operation.

Fabric Control Plane Operation:

Fabric Control Plane has following Functions.

  • It registers all the End points connected to Edge nodes and also tracks their location in the fabric.
  • It replies to queries from network elements about location of end points in the fabric
  • When any end points are moved from one location to another, it ensures that traffic is redirected to current location.

Below Figure describes about control plane operation.


  1. As soon as End point 1 is connected to edge 1, it will be registered to the fabric control plane node. The registration includes End point 1's IP address, MAC address, and location that is fabric switch edge 1.
  2. Likewise as soon as End point 2 gets connected on edge 2, it will also be registered to the fabric control plane node. The registration includes End point 2's IP ad dress, MAC address, and its location that is fabric switch edge 2.
  3. Now let’s see when End point 1 wants to communicate to End point 2, edge 1 on which Endpoint 1 is connected on receipt of packet will query the fabric control plane node for the location of End point 2.
  4. Once the Edge 1 gets the reply from Control plane node that is (End point 2 location is behind edge 2 ) it will encapsulate the traffic from End point 1 using VXLAN, and send it to End point 2 (via edge 2).
  5. Once the traffic arrives at edge 2, it will be decapsulated at Edge 2 and forwarded along to End point 2.
  6. The reverse applies when End point 2 wants to communicate back to End point 1.

Data Plane Forwarding:

Data Plane forwarding is done on VXLAN Overlay network. Below figure describes the Data Plane forwarding in a VXLAN encapsulated network.

SD- Access fabric uses the same semantics of Layer 2 or Layer 3 forwarding and allows

the fabric edge nodes to perform overlay routing or bridging functions based on packet type.

  • Layer 2 virtual network interface (L2 VNI): In this mode, frames from an L2 VNI are bridged to another L2 interface.
  • Layer 3 virtual network interface (L3 VNI): In this mode, frames from an L3 VNI are routed to another L3 interface. The routing will be done with in the context of a routing in stance.  If Traffic from one subnet to be routed to another subnet, it uses Distributed Anycast Default Gateway and this gateway will be provisioned on every Edge node in fabric.

SD-Access Wireless:

There are two way, by which Wireless can be integrated in SD-Access.

  • SD-Access Wireless: It provides full wireless integration in to fabric.
  • Traditional Wireless or Over the Top (OTT): Legacy wireless traffic need to be taken over the fabric.

SD-Access Wireless : Fabric WLC notifies the fabric Control plane node about all Wireless Clients joins , Roams and disconnects due to which the Fabric Control plane node has all information about wired and wireless uses in fabric.

In data Plane function, Fabric WLC asks the fabric AP to form the VXLAN overlay tunnel to all other adjacent fabric Edge Nodes. This Tunnel is used to carry all the segmentation and policy information to /from fabric nodes to provide communication between wireless and wired nodes.

Now let’s see how traffic flow works between them. As soon as Wireless clients joins the fabric over fabric AP, Fabric WLC will onboard the endpoint and inform to fabric Control plane node with its MAC address. Now WLC will ask Fabric AP to build the VXLAN tunnel to its adjacent node. Once it is done, Wireless client will get the IP address from DHCP and then Edge node will register its IP address to its control plane node. And then traffic will start flowing.

The Fabric WLC can be located or connected to external border node or may be at Data Center, however IP Subnet prefix of WLC must be advertised in to underlay routing domain , which will be used for AP onboarding and management via traditional CAPWAP control plane.

As AP are connected to Fabric Edge node or it may also be connected to SD-Access Extended nodes. Only notable point is latency between fabric WLC and AP should be 20 ms or less.  

As Soon as Fabric capability is enabled on WLC, Fabric AP will follow these below step to join in to network.


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