- [Instructor] The SDA overlay is a beautiful thing.
As an endpoint sends a frame to the first SDA node,
the node will encapsulate the frame
into a VXLAN tunnel and forward it to the next SDA node.
At this point, the SDA nodes will continue
to forward the frame based on its VXLAN tunnel information
until it hits the last SDA node,
which decapsulates it from its VXLAN wrapper
and delivers it to the endpoint destination.
All of this encapsulation and decapsulation
actually happens within the switches' ASICs,
so there's no performance penalty
since it's done in hardware.
The endpoint learning and forwarding process
goes as follows in an SDA network.
First, fabric edge nodes connecting the endpoint devices
learn endpoint IPs and MACs in the normal fashion,
and create a unique endpoint identifier or EID
for each endpoint.
As this EID is learned, it's then communicated
to a centralized database called the LISP map server.
The LISP map server maintains a list of the EIDs
and their corresponding routing locators, or RLOCs.
Last, the fabric data plan can then use
the LISP map server to forward packets
to the proper destination.
That's a lot of terminology in a short time.
Here's a quick example.
Switch two and three have already forwarded packets
between then, so they've already informed
the LISP map server of their EIDs,
so it's already got a record of them.
Switch one has a new packet enter,
sourced from 192.168.1.2, destined for 192.168.2.2,
which loads off of switch two.
At this point, switch one will query the LISP map server
on how to reach 2.2.
The LISP server sees an entry for that destination
listing two as the RLOC,
so it will contact switch three to confirm.
Switch two will then inform switch one
that 192.168.2.2 is reachable via itself.
Switch one will now encapsulate the traffic
within VXLAN, and set the VXLAN destination headers
to be the RLOC of switch two and forward the traffic.
While this process may seem a little involved,
it's all hidden behind DNA Center,
so engineers can focus on policies
rather than delivery of packets.
The overlay is likely the most foreign topic
for new engineers, so additional research on this topic
wouldn't be a waste of time.