In the Virtual Router Redundancy Protocol (VRRP), the Master router is responsible for forwarding packets sent to the virtual router's IP address. To facilitate this, the Master must respond to ARP requests for the virtual IP with the associated virtual MAC address and forward any frames arriving at that virtual MAC. Conversely, a Backup router monitors the Master's status but must remain passive in the data plane to prevent duplicate traffic or IP conflicts. Therefore, a Backup router must not respond to ARP requests for the virtual IP and must discard any packets destined for the virtual MAC address (unless it transitions to the Master state).

IETF RFC 3768, "Virtual Router Redundancy Protocol (VRRP)", Section 6.4.2 (Backup): States that the Backup router "MUST NOT respond to ARP requests for the IP address(es) associated with the virtual router" and "MUST discard packets with a link layer destination MAC address equal to the virtual router MAC address."

IETF RFC 3768, "Virtual Router Redundancy Protocol (VRRP)", Section 6.4.3 (Master): States that the Master router "MUST respond to ARP requests for the IP address(es) associated with the virtual router" and "MUST forward packets with a link layer destination MAC address equal to the virtual router MAC address."

Cisco Systems, "First Hop Redundancy Protocols Configuration Guide, Cisco IOS Release 15M&T", Chapter: VRRP, Section: "VRRP Operation".

Juniper Networks, "Junos OS High Availability Library for Routing Devices", Section: Understanding VRRP, Subsection: "VRRP Router Priority and Preemption".