If you want use public ip addresses you need at least  2.  For mx1wan1 and mx2 wan1.   If you want to use a WAN-VIP address ( This ip is only active on the active mx) you need 1 more public IP (3x IP)   If you can only get 1 Public IP from the provider you could use a NAT router between provider and mx,  and use private range addresses on the MX   Wan ip can be set static or from dhcp ... View more