A primary address is an IP address selected from the set of real interface address. VRRP advertisements are always sent using the primary IP address as the source of the IP packet.
An IP interface must always have a primary IP address assigned for VRRP to be active on the interface. Nokia routers supports both primary and secondary IP addresses (multi-netting) on the IP interface. The virtual router’s VRID primary IP address is always the primary address on the IP interface. VRRP uses the primary IP address as the IP address placed in the source IP address field of the IP header for all VRRP messages sent on that interface.