Difference between Underlay and Overlay Networks
Today I am
going to talk about the underlay and overlay networks and protocol used for these
purposes. Most of the software defined networks are based on the underlay and
overlay both in order to achieve the separate control and data planes in the
network. Earlier we have the control and data plane within the same physical
boxes but now separating data plane with the control plane is a huge shift of
the design now a days.
As many of
you already know about the underlay networks or so called Physical networks where
your traditional protocols are working. Let’s talk a little on underlay network.
Underlay network
The
underlay network is described by the physical devices and can be switches and
routers in the network. All network components of the underlay must determine
IP connectivity via the use of a routing protocol. The protocol used on the underlay
devices are like OSPF, IS-IS, BGP for routing purposes.
For
underlay network to setup a well-designed Layer 3 foundation inclusive of the
campus edge switches to ensure performance, scalability, and high availability
of the network.
Though
there are many alternative routing protocols, the IS-IS selection offers
operational advantages such as neighbor establishment without IP protocol
dependencies, peering capability using loopback addresses, and agnostic
treatment of IPv4, IPv6, and non-IP traffic.
Underlay
Protocols : BGP, OSPF, IS-IS, EIGRP
Hope you understand
the basics of the underlay network, Now let’s talk about the Overlay network
which makes SDN story by automate the configuration through the controller.
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Fig 1.1- Underlay and Overlay Networks
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Overlay network
An overlay
network is formed on top of the underlay in direction to construct a
virtualized network. The data plane traffic and control plane signaling is controlled
within each virtualized network, upholding segregation between the networks in accumulation
to freedom from the underlay network. Most of the instances you generate fabric
by implements virtualization and encapsulating user traffic in overlay networks
using IP packets that are sourced and ended at the boundaries of the fabric.
The fabric
boundaries comprise borders for incoming and outgoing to a fabric, fabric edge
switches for wired clients, and fabric APs for wireless clients. Overlay
networks can run across all or a subset of the underlay network devices.
Numerous
overlay networks can run through the same underlay network to provision
multitenancy through virtualization. Each overlay network performs as a Virtual Routing and Forwarding (VRF) instance for joining to external networks. You reserve
the overlay separation when spreading the networks outside of the fabric by
using VRF-lite, preserving the network separation within devices associated to
the fabric and also on the links between VRF-enabled devices.
Overlay Protocols
: VXLAN, NVGRE, GRE, OTV, OMP, mVPN and many more.
