Device | Comparison process | Configuration BPDU on | ||
ports after comparison | ||||
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| ∙ Port BP1 receives the configuration BPDU of Device A {0, 0, 0, |
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| AP1}. Device B finds that the received configuration BPDU is |
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| superior to the configuration BPDU of the local port {1, 0, 1, |
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| BP1}, and updates the configuration BPDU of BP1. | BP1: {0, 0, 0, AP1} | |
| ∙ | Port BP2 receives the configuration BPDU of Device C {2, 0, 2, | ||
| BP2: {1, 0, 1, BP2} | |||
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| CP2}. Device B finds that the configuration BPDU of the local | ||
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| port {1, 0, 1, BP2} is superior to the received configuration |
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| BPDU, and therefore discards the received configuration |
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| BPDU. |
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| ∙ Device B compares the configuration BPDUs of all its ports, and |
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Device B |
| determines that the configuration BPDU of BP1 is the optimum |
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| configuration BPDU. Then, it uses BP1 as the root port, the |
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| configuration BPDUs of which will not be changed. |
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| ∙ | Based on the configuration BPDU of BP1 and the path cost of | Root port BP1: | |
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| the root port (5), Device B calculates a designated port | {0, 0, 0, AP1} | |
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| configuration BPDU for BP2 {0, 5, 1, BP2}. | ||
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| Designated port BP2: | ||
| ∙ | Device B compares the calculated configuration BPDU {0, 5, 1, | ||
| {0, 5, 1, BP2} | |||
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| BP2} with the configuration BPDU of BP2. If the calculated | ||
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| BPDU is superior, BP2 will act as the designated port, and the |
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| configuration BPDU on this port will be replaced with the |
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| calculated configuration BPDU, which will be sent out |
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| periodically. |
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| ∙ Port CP1 receives the configuration BPDU of Device A {0, 0, 0, |
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| AP2}. Device C finds that the received configuration BPDU is |
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| superior to the configuration BPDU of the local port {2, 0, 2, |
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| CP1}, and updates the configuration BPDU of CP1. | CP1: {0, 0, 0, AP2} | |
| ∙ | Port CP2 receives the configuration BPDU of port BP2 of Device | ||
| CP2: {1, 0, 1, BP2} | |||
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| B {1, 0, 1, BP2} before the configuration BPDU is updated. | ||
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| Device C finds that the received configuration BPDU is superior |
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| to the configuration BPDU of the local port {2, 0, 2, CP2}, and |
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| therefore updates the configuration BPDU of CP2. |
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| After comparison: |
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| ∙ The configuration BPDU of CP1 is elected as the optimum |
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| configuration BPDU, so CP1 is identified as the root port, the | Root port CP1: | |
Device C |
| configuration BPDUs of which will not be changed. | {0, 0, 0, AP2} | |
| ∙ Device C compares the calculated designated port | |||
| Designated port CP2: | |||
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| configuration BPDU {0, 10, 2, CP2} with the configuration | ||
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| {0, 10, 2, CP2} | ||
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| 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 |
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| 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 | ||
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| BPDUs from Device A. Device C does not launch an update |
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| process after comparison. |
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