Planet GS-5220 User Manual page 165

The switch with the lowest Bridge ID (switch C) was elected the root bridge, and the ports were selected to give a high port cost
between switches B and C. The two (optional) Gigabit ports (default port cost = 20,000) on switch A are connected to one
(optional) Gigabit port on both switch B and C. The redundant link between switch B and C is deliberately chosen as a 100
Mbps Fast Ethernet link (default port cost = 200,000). Gigabit ports could be used, but the port cost should be increased from
the default to ensure that the link between switch B and switch C is the blocked link.
User's Manual of GS-5220 PoE Series Managed Switch
165