Virtual MAC address assignment
In load balancing mode, the master assigns virtual MAC addresses to routers in the VRRP group. The master uses different MAC addresses to respond to ARP requests or ND requests from different hosts. The backup routers, however, do not answer ARP requests or ND requests from hosts.
In an IPv4 network, a load balanced VRRP group works as follows:
The master assigns virtual MAC addresses to all member routers, including itself. This example assumes that the virtual IP address of the VRRP group is 10.1.1.1/24, Router A is the master, and Router B is the backup. Router A assigns 000f-e2ff-0011 for itself and 000f-e2ff-0012 for Router B. See Figure 17.
Figure 17: Virtual MAC address assignment
When an ARP request arrives, the master (Router A) selects a virtual MAC address based on the load balancing algorithm to answer the ARP request. In this example, Router A returns the virtual MAC address of itself in response to the ARP request from Host A. Router A returns the virtual MAC address of Router B in response to the ARP request from Host B. See Figure 18.
Figure 18: Answering ARP requests
Each host sends packets to the returned MAC address. As shown in Figure 19, Host A sends packets to Router A and Host B sends packets to Router B.
Figure 19: Sending packets to different routers for forwarding
In the ARP reply sent by the master, the source MAC address in the Ethernet header is different from the sender MAC address in the message body. For the Layer 2 device to forward the ARP packet, follow these configuration guidelines on the Layer 2 device:
Do not enable ARP packet source MAC address consistency check.
Do not specify the src-mac keyword when you enable ARP packet validity check for ARP detection.
For more information about ARP packet source MAC address consistency check and ARP detection, see Security Configuration Guide.