Currently BGP sessions for Layer 3 management networks are limited to the primary / first IP of the network.

If a user deploys a server with a larger subnet size such as /29 it's not possible to have BGP sessions from the other IPs inside the same subnet. It has to be the first available host IP.

This is useful for certain situations such as deploying a virtual network functions appliance or Google Anthos Layer 3 bundled load balancers with BGP.