When enable_isolated_metadata is set to True and the gateway for a subnet is not set or is not a Neutron router, the DHCP service is capable of injecting a route to the metadata service via the classless-static-route DHCP option, also known as option 121.

Once an instance connected to a subnet with the mentioned characteristics has been created, observe the following routes passed to the instance via DHCP:

The next hop address for the metadata route is the IP address of the DHCP server that responded to the initial DHCP request from the client. If there were multiple DHCP agents in the environment and the same network was scheduled to all of them, it is possible that the next hop address would vary between instances, as any of the DHCP servers could have responded to the request.