Cisco Design Guide

Layer 2 Border Handoff provides an overlay service between the SD-Access network and the traditional network, allowing hosts in both to communicate, ostensibly, at Layer 2.  When a traditional network is migrating to an SD-Access network, the Layer 2 Border Handoff is a key strategic feature.  Endpoints can remain in place in the traditional network while communication and interaction are tested with the endpoints in the fabric without needing to re-IP address these hosts.  Hosts can then be migrated over to fabric entirely either through a parallel migration which involves physically moving cables or through an incremental migration of converting a traditional access switch to an SD-Access fabric edge node.

The Layer 2 Border Handoff allows the fabric site and the traditional network VLAN segment to operate using the same subnet.  Communication between the two is provided across the border bode with this handoff that provides a VLAN translation between fabric and non-fabric.  Cisco DNA Center automates the LISP control plane configuration along with the VLAN translation, Switched Virtual Interface (SVI), and the trunk port connected to the traditional network on this border node.

Multicast is supported across the Layer 2 handoff, allowing multicast communication between the traditional network and the SD-Access network.  The multicast forwarding logic operates the same across the Layer 2 handoff border node as it does in the fabric, as described in the multicast Forwarding section, and the traditional network will flood multicast packets using common Layer 2 operations.

For OT (Operational Technology), IoT, and BMS (Building Management Systems) migrating to SD-Access, the Layer 2 border handoff can be used in conjunction with Layer 2 Flooding.  This enables Ethernet broadcast WoL capabilities between the fabric site and the traditional network and allows OT/BMS systems that traditionally communicate via broadcast to migrate incrementally into the fabric.