How does Citrix ADC communicate IP-to-MAC address bindings that have changed to switches and routers during a failover of an HA pair?

• A. The Citrix ADC uses MAC-based Forwarding to update the routers.
• B. The Citrix ADC uses Gratuitous ARPs (GARPs) to update the devices on the network
• C. The Citrix ADC uses Reverse ARP (RARP) to update the devices on the network.
• D. The Citrix ADC uses Proxy ARP to update the devices on the network.

Answer: (B)

Gratuitous ARP is an unsolicited ARP announcement that refreshes the network’s understanding of which MAC address is associated with a given IP. In a failover of an HA Citrix ADC pair, the virtual IP (VIP) continues to be the same, but the MAC address on the active device can change. Switches and routers keep ARP caches for efficiency, so they need to learn the new IP-to-MAC mapping right away. The new active ADC sends a Gratuitous ARP for the VIP, which updates all devices’ ARP tables, ensuring traffic is directed to the current active node without waiting for normal ARP traffic to refresh entries. Other mechanisms either don’t provide the same network-wide ARP refresh or are used for different purposes, so Gratuitous ARP is the correct way to propagate the binding change during failover.