3Com WX3000 operation manual Device Comparison process Bpdu of port after

Device	Comparison process	BPDU of port after
		comparison
	z Port CP1 receives the configuration BPDU of Device A {0, 0,
	0, AP2}. Device C finds that the received configuration BPDU
	is superior to the configuration BPDU of the local port {2, 0, 2,
	CP1}, and updates the configuration BPDU of CP1.	CP1: {0, 0, 0, AP2}
	z Port CP2 receives the configuration BPDU of port BP2 of
		CP2: {1, 0, 1, BP2}
	Device B {1, 0, 1, BP2} before the message was updated.
	Device C finds that the received configuration BPDU is
	superior to the configuration BPDU of the local port {2, 0, 2,
	CP2}, and updates the configuration BPDU of CP2.
	By comparison:
	z The configuration BPDUs of CP1 is elected as the optimum	Root port CP1:
	configuration BPDU, so CP1 is identified as the root port, the
		{0, 0, 0, AP2}
	configuration BPDUs of which will not be changed.
		Designated port
	z Device C compares the calculated designated port
	configuration BPDU {0, 10, 2, CP2} with the configuration	CP2:
	BPDU of CP2, and CP2 becomes the designated port, and	{0, 10, 2, CP2}
	the configuration BPDU of this port will be replaced with the
	calculated configuration BPDU.
Device C	z Next, port CP2 receives the updated configuration BPDU of
	Device B {0, 5, 1, BP2}. Because the received configuration
	BPDU is superior to its old one, Device C launches a BPDU	CP1: {0, 0, 0, AP2}
	update process.
		CP2: {0, 5, 1, BP2}
	z At the same time, port CP1 receives configuration BPDUs
	periodically from Device A. Device C does not launch an
	update process after comparison.
	By comparison:
	z Because the root path cost of CP2 (9) (root path cost of the
	BPDU (5) + path cost corresponding to CP2 (4)) is smaller
	than the root path cost of CP1 (10) (root path cost of the
	BPDU (0) + path cost corresponding to CP2 (10)), the BPDU	Blocked port CP2:
	of CP2 is elected as the optimum BPDU, and CP2 is elected
		{0, 0, 0, AP2}
	as the root port, the messages of which will not be changed.
		Root port CP2:
	z After comparison between the configuration BPDU of CP1
	and the calculated designated port configuration BPDU, port	{0, 5, 1, BP2}
	CP1 is blocked, with the configuration BPDU of the port
	remaining unchanged, and the port will not receive data from
	Device A until a spanning tree calculation process is
	triggered by a new condition, for example, the link from
	Device B to Device C becomes down.

After the comparison processes described in the table above, a spanning tree with Device A as the root bridge is stabilized, as shown in Figure 1-3.

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