When is GLBP preferred over HSRP?

GLBP (Gateway Load Balancing Protocol) is preferred when you need to load-balance traffic across multiple gateways using a single virtual IP address. Unlike HSRP (Hot Standby Router Protocol), which uses an active/standby model with only one active gateway forwarding traffic, GLBP allows all gateways in a group to actively forward traffic. It achieves this by assigning a unique virtual MAC address to each active forwarder, all associated with the same virtual IP. The other options are incorrect: GLBP is a Cisco proprietary protocol, so it's not suitable for mixed Cisco and non-Cisco environments (VRRP would be better). GLBP does not inherently provide encrypted hellos; security features are typically implemented at a different layer. GLBP assigns different virtual MAC addresses to each active forwarder, so clients would not see the same MAC address across multiple gateways.