When you update the Domain Name System (DNS) parameters or static routes for a subnet, you must take extra steps to make the
changes visible at a particular port or instance. We recommend that you use one of the two following sets of steps:
Associate and then disassociate the affected port with a dummy security group.
A dummy security group is an extra security group that you add to any security groups already configured on the port. The
dummy security group does not need to contain any rules.
Set the adminstrative state of the affected port to down, and then set the state to up.
Either set of steps triggers an update notification for the port, which allows the port to start using the changed parameters.