Connecting SD-Access and Legacy Network

[legacynetwork]

Our client wants to retain couple of existing L2 switches while also introducing new DNAC Fabric into LAN. 

Current Topology : WAN Router > Core > Access
New Topology : WAN Router>New Firepower x 2>New Core Switch x 2>New Access Switch x 5
IP Schema : Retain half of existing subnets and have some new. 

There are now 5 L2 switches on the site. The customer wants connections moved from 3switches to new access switches, but they also want to retain 2 switches. In a year, those will be replaced.

Do we now need to create a trunk and pass those VLANS between the new core and the existing core in order for the legacy and new networks to coexist? And how users at the old access switch still able to authenticate with ISE? Is it feasible? ? Any thoughts?

[Torbjørn]

You can have the old L2 network and the new SDA fabric co-exist using a L2 border handoff. You can read more about this in the "Migration to SD Access" portion of the CVD: https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/cisco-sda-design-guide.html#Layer2BorderHandoff 

[Andrii Oliinyk]

assuming that u would like to reuse Anycast GW property of the LISP/VXLAN Fabric u could implement 2 legacy switches as Extended Policy Node attached to 3 switches migrated to SDA (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi_9Ku12LKHAxWiR_EDHRyyAIgQwqsBegQIFBAF&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D0DoqgWjFDkU&usg=AOvVaw1WO3cUAtAXIzVsrpSugZO5&opi=89978449). Check if the switches HW is compatible with Cisco Software-Defined Access Compatibility Matrix .