Explanation/Reference: https://www.checkpoint.com/products/application-control-software-blade/

Explanation
Each instance of VRRP running on a supported interface may monitor the link state of other interfaces. The monitored interfaces do not have to be running VRRP.
If a monitored interface loses its link state, then VRRP will decrement its priority over a VRID by the specified delta value and then will send out a new VRRP HELLO packet. If the new effective priority is less than the priority a backup platform has, then the backup platform will beging to send out its own HELLO packet.
Once the master sees this packet with a priority greater than its own, then it releases the VIP.

IP spoofing replaces the untrusted source IP address with a fake, trusted one, to hijack connections to your network. Attackers use IP spoofing to send malware and bots to your protected network, to execute DoS attacks, or to gain unauthorized access.
Reference:
http://dl3.checkpoint.com/paid/74/74d596decb6071a4ee642fbdaae7238f/
CP_R80_SecurityManagement_AdminGuide.pdf?
HashKey=1479584563_6f823c8ea1514609148aa4fec5425db2&xtn=.pdf