HP manual 196

Device	Comparison process	Configuration BPDU on
		ports after comparison
	After comparison:
	• The configuration BPDU of CP1 is elected as the optimum
	configuration BPDU, so CP1 is identified as the root port, the	• Root port CP1: {0, 0,
	configuration BPDUs of which will not be changed.
		0, AP2}
	• Device C compares the calculated designated port
		• Designated port CP2:
	configuration BPDU {0, 10, 2, CP2} with the configuration
		{0, 10, 2, CP2}
	BPDU of CP2, and CP2 becomes the designated port, and
	the configuration BPDU of this port will be replaced with the
	calculated configuration BPDU.

•Then, port CP2 receives the updated configuration BPDU of

Device B {0, 5, 1, BP2}. Because the received configuration
BPDU is superior to its own configuration BPDU, Device C	• CP1: {0, 0, 0, AP2}
launches a BPDU update process.
	• CP2: {0, 5, 1, BP2}
• At the same time, port CP1 receives periodic configuration
BPDUs from Device A. Device C does not launch an update
process after comparison.
After comparison:
• Because the root path cost of CP2 (9) (root path cost of the
BPDU (5) plus 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: {0,
of CP2 is elected as the optimum BPDU, and CP2 is elected
as the root port, the messages of which will not be changed.	0, 0, AP2}
• After comparison between the configuration BPDU of CP1	• Root port CP2: {0, 5,
and the calculated designated port configuration BPDU,	1, BP2}
port CP1 is blocked, with the configuration BPDU of the port
unchanged, and the port will not receive data from Device A
until a spanning tree calculation process is triggered by a
new event, for example, the link from Device B to Device C
going down.

After the comparison processes described in Table 56, a spanning tree with Device A as the root bridge is established, and the topology is as shown in Figure 175.

Figure 175 The final calculated spanning tree

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