Planet Technology WGSW-24040R, SGSW-24040R user manual 110

				User’s Manual of WGSW-24040 / WGSW-24040R
					SGSW-24040 / SGSW-24040R
			LAN 1
			Portcast = 19
	A		Port 3
		Bridge ID = 15
	Port 1		Port 2
	Portcast = 4			Portcast = 4
	Portcast = 4			Portcast = 4
B	Port 1			C	Port 1
Bridge ID = 30				Bridge ID = 20
Port 2	Port 3	Portcast = 19		Port 2	Port 3
	Portcast = 19				Portcast = 19
	LAN 2				LAN 3

Figure 4-7-5Before Applying the STA Rules

In this example, only the default STP values are used.

		LAN 1
	A	Port 3
		Root Bridge
	Port 1		Port 2
	Designated Port		Designated Port
	Root Port		Root Port
B	Port 1		C	Port 1
			Designated Bridge
Port 2	Port 3	Blocked	Port 2	Port 3
	LAN 2			LAN 3

Figure 4-7-6After Applying the STA Rules

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 = 4) 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 = 19). 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.

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