The Cisco Systems Giga Stack Gigabit Interface Converter (GBIC) is a versatile, low-cost, Gigabit Ethernet stacking GBIC that offers high-speed interconnectivity between Catalyst 3500 series XL & modular Catalyst 2900 series XL switches. Equipped with two 1000 Base X Gigabit Ethernet ports, the Giga Stack GBIC provides a hardware-based, independent stack bus with 1-Gbps forwarding bandwidth in a daisy-chained configuration, or up to 2-Gbps forwarding rate in a point-to-point, full-duplex configuration. For customers who want a low-cost stacking solution, the Giga Stack GBIC delivers a shared 1-Gbps stacking bus to connect up to nine Catalyst 3500XL & gigabit-enabled Catalyst 2900XL switches in a daisy-chain configuration. By inserting secondary Giga Stack GBICs, users can create a redundant loopback connection from the top to the bottom of the stack. For the highest performance stacking, the Catalyst 3508G XL can be deployed with Giga Stack GBICs to aggregate up to eight Catalyst 3500XL & gigabit-enabled Catalyst 2900XL switches in a Gigabit Ethernet star topology.