ARP and VRRP control packets

Source MAC addresses in VRRP control packets

• VRRP—The virtual MAC address is the source.
• VRRP-E—The physical MAC address is the source.

VRRP control packets

• VRRP—Control packets are IP type 112 (reserved for VRRP), and they are sent to the VRRP multicast address 224.0.0.18.
• VRRP-E—Control packets are UDP packets destined to port 8888, and they are sent to the all-router multicast address 224.0.0.2.

Gratuitous ARP

When a VRRP device (either master or backup) sends an ARP request or a reply packet, the MAC address of the sender is the MAC address of the router interface. One exception is if the owner sends an ARP request or a reply packet, in which case the MAC address of the sender is the virtual MAC address. Only the master answers an ARP request for the virtual router IP address. Any backup router that receives this request forwards the request to the master.

• VRRP—A control message is sent only once when the VRRP device assumes the role of the master.
• VRRP-E—A control message is sent every 30 seconds by the VRRP-E master device because VRRP-E control packets do not use the virtual MAC address.