For IPv4 traffic, a primary IPv4 address is selected from the set of real interface addresses. VRRP (Virtual Router Redundancy Protocol) advertisements are always sent using the primary IPv4 address as the source of the IPv4 packet.
The VRRP MAC address for an IPv4 VRRP router instance is an IEEE 802 MAC address in the following hexadecimal format (in Internet-standard bit-order):
00-00-5E-00-01-<vrid>
The first three octets are derived from the IANA Organizational Unique Identifier (OUI). The next two octets (00-01) indicate the address block assigned to the VRRP router for the IPv4 protocol, and VRID is the VRRP instance identifier. This mapping provides for up to 255 IPv4 VRRP routers on a network.
When a VRRP router instance becomes active, the master router issues a gratuitous ARP response that contains the VRRP router MAC address for each VRRP router IP address.
The master also always responds to ARP requests for VRRP router IP addresses with an ARP response containing the VRRP MAC address. Hosts on the network use the VRRP router MAC address when they send traffic to the default gateway.
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