When implementing seamless VXLAN stitching between two data centers, the Ethernet Segment Identifier (ESI) must match in both data centers to ensure that the same multi-homed segment is recognized consistently across the environments. This allows seamless failover and redundancy. However, the translation VNI (Virtual Network Identifier) must be different in each data center because VXLAN stitching involves mapping different VNIs to enable interconnectivity between distinct VXLAN domains.
If the same translation VNI is used in both data centers, there would be no differentiation between network segments, leading to potential routing and forwarding issues. Keeping them different ensures proper traffic isolation and mapping.