If someone has an automated way of accomplishing this I'd be interested too. We typically just manually disable the guest network when the primary goes down. To avoid them using the limited bandwidth on the backup connection. Maybe there is a solution where would create a route or preference where the guest network only uses the primary I'd just be skeptical that it still wouldn't try to use the secondary if the primary goes down.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO If this was helpful click the Kudo button below If my reply solved your issue, please mark it as a solution.