What actually means Fabric Network or Cisco Fabric in real scenarios

[ahmedaburaihan]

Hello Everyone!

I had confusion regarding Fabric. I have read that Fabric means a meshed network of devices consisting of Overlay and Underlay. But isn't it the actual network? then what's the difference between a Fabric and 

[Giuseppe Larosa]

Hello @ahmedaburaihan ,

The Fabric is actually a L3 IP routed network that builds the underlay, that provides connectivity between edge devices.

In the case we use an overlay with VXLAN encapsulation, the fabric provides IP connectivity between VTEP loopback addresses using links with increased MTU in order to be able to carry an ethernet frame with the 50/54 bytes overhead of VXLAN encapsulation without using IP fragments.

An IGP routing protocol is used and the most recommended and deployed is IS-IS with some multicast forwarding extensions.

The overlay then provides the services L2 and L3 connectivity between VXLAN segments hosted on VTEPs.

The control plane can use a data driven approach using PIM Bidir  or it can use MP BGP EVPN address family to advertise MAC addresses and IP addresses of endpoints within a context ( VNID ).

Hope to help

Giuseppe