Underlay Vs Overlay Networks

Next Generation networks talk about the Overlay networks and traditional networks are basically using underlay. Now it is important to understand both technologies and how they are interoperated and works together.

Underlay Networks
Network switches and routers are physical devices that make up the underlay network. Routing protocols must be used by all network components of the underlay to determine IP connectivity. As far as routing protocols are concerned, the underlay devices use OSPF, IS-IS, and BGP.

The overlay network is built on top of the overlay network, which is the physical infrastructure. Packets are delivered across networks through this underlying network.

Fig 1.1- Underlay Vs Overlay Networks

Overlay Networks
In order to construct a virtualized network, an overlay network is constructed on top of the underlay. A virtualized network isolates the data plane traffic and control plane signaling to ensure freedom from the underlay network.

The majority of fabric instances use virtualization and encapsulate user traffic in overlay networks using IP packets that originate and terminate at the fabric boundaries.

Some of the overlay networks are VXLAN, NVGRE, GRE, OTV, OMP and mVPN.

Difference between Underlay and Overlay Networks
Lets talk about the difference, below is the table showing the difference between underlay and overlay networks in details.