- [Presenter] In an effort to redesign
the way campus networks are built,
Cisco developed Software-Defined Access or SDA.
It's an ecosystem with switches and routers, but at its core
sits the Digital Network Architecture Center Controller
or DNA Center.
DNA provides a GUI and APIs for an administrator
to manage an SDA network.
DNA southbound interface contains
an overlay, underlay, and fabric.
The underlay are the physical devices and the cables
used to tie them together.
Their sole mission is to dynamically discover
SDA endpoints and devices.
The overlay's responsibility is to create
Virtual Extensible LAN or VXLAN tunnels
between SDA switches to transport traffic
across the fabric.
The fabric is the marrying of the underlay and the overlay
that transport data over the network.
While the underlay network may look something like this
with many interconnected switches,
the overlay creates VXLAN tunnels
that will deliver traffic more like this.
SDA underlay is more easily applied to a brand-new network
so that the DNA Center can fully configure and control
the infrastructure without fear of disruption.
When configuring SDA on an existing network,
all of the equipment in use must be
on the hardware compatibility list
to ensure proper interoperability.
The correct software must be installed
to support the desired roles and features.
At the time of this writing,
DNA Center should not be used to configure
the underlay of any in-production equipment.
The fabric edge node connects to endpoint devices
in much the same way a traditional switch would.
A fabric border node is a switch that connects
to anything not directly within the control of SDA,
and this could be an ACI Data Center or a WAN device.
A fabric control node is a switch that performs
special functions for the control plane,
often requiring both additional RAM and CPU resources.
Building a new SDA network can be considerably simpler,
as an engineer can focus on ordering the correct hardware
and software, and then just letting DNA Center
do the configuration work for the underlay.
In a traditional switch network edge,
switches would utilize something like this
where they connect via redundant links upstream,
letting RSTP protect against loops.
They generally also utilize a first hop redundancy protocol
like HSRP to act as gateway redundancy.
A brand-new SDA fabric would instead
use a routed access layer design.
As the name implies, the access switches
would use routed layer three links
back to the core of the network
as opposed to purer layer two links.
In addition to each switch routing
towards the core of the network,
they also use the IS-IS routing protocol.
Doing away with layer two links
means RSTP is no longer necessary.
In this configuration, the SDA edge node
can now act as the default gateway for the endpoint devices,
so a first hop redundancy protocol is no longer necessary.