Protocol carp: How does VIP work?

Question

FreeBSD

Good day to all!
For personal tests and needs, there is a need to build a failover router based on Pfsense.
Faced a misunderstanding of how the VIP address works, for example:
I have 2 providers, each issued 2 white IPs. For carp to work, you need 1 more VIP that will link to 2 main ones.
Questions:
1. How to get this VIP address?
2. Should providers make any settings (providers are different)?

Answer 1

You need at least 3 addresses from each provider. The address groups of each of the providers must be in the same l2 network.