VXLAN - VLAN to VNI mapping

The purpose of VXLANs is not only to surpass the limitation of 4K VLAN IDs, but also to add flexibility to deployments, allowing for the simpler spanning of VLANs across sites. When there is no need to expand beyond that 4K limit, typical customer deployments will use a 1:1 mapping of available VLANs for simplicity.

However, when scalability to reach beyond this limit is needed, then it is possible to do so by assigning the same VLAN IDs to multiple unique VNIs found on different VTEPs within the fabric. So for example, you could have

  • VLAN 456 mapped to VNI 123 using a subnet of 10.1.1.0/24
  • VLAN 456 mapped to VNI 321 using a subnet of 10.2.2.0/24

So in a VXLAN implementation, the 4k VLANs in a single switch is still a limitation locally, but across the fabric, it is the VNI that is significant, and that is a 24 bit value providing over 16 million VNIs.

https://networklessons.com/cisco/ccnp-encor-350-401/introduction-to-virtual-extensible-lan-vxlan