A VNI mismatch breaks the overlay even when the two underlay addresses still communicate.

VXLAN needs matching tunnel parameters as well as a working underlay

VXLAN carries an Ethernet frame inside a UDP packet so an overlay network can cross an IP underlay. Tunnel endpoints encapsulate and decapsulate frames, while a 24-bit VXLAN Network Identifier, or VNI, identifies the virtual segment. The outer IP addresses route between endpoints; the inner Ethernet and IP addresses serve the overlay. These are separate layers with separate reachability and configuration requirements. ...

October 28, 2027 · 5 min · XB Field Notes