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QSW-2900-24T-AC
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Qtech QSW-2900-24T-AC Руководство пользователя онлайн [147/209] 481595

10-145

Device Comparison process

BPDU of port after

comparison

· Port CP2 receives the configuration BPDU of port

BP2 of 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:

· The configuration BPDUs of CP1 is elected as the

optimum configuration BPDU, so CP1 is identified as

the root port, the configuration BPDUs of which will

not be changed.

· Device C compares the computed designated port

configuration BPDU {0, 10, 2, CP2} with the

configuration BPDU of CP2, and CP2 becomes the

designated port, and the configuration BPDU of this

port will be replaced with the computed configuration

BPDU.

Root port CP1:

{0, 0, 0, AP2}

Designated port

CP2:

{0, 10, 2, CP2}

· 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 update process.

· At the same time, port CP1 receives configuration

BPDUs periodically from Device A. Device C does

not launch an update process after comparison.

CP1: {0, 0, 0, AP2}

CP2: {0, 5, 1, BP2}

By comparison:

· 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 of CP2 is

elected as the optimum BPDU, and CP2 is elected as

the root port, the messages of which will not be

changed.

· After comparison between the configuration BPDU

of CP1 and the computed designated port

configuration BPDU, port 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 computing process is

triggered by a new condition, for example, the link

from Device B to Device C becomes down.

Blocked port CP2:

{0, 0, 0, AP2}

Root port CP2:

{0, 5, 1, BP2}

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 3.

Qtech QSW-2900-24T-AC Руководство пользователя онлайн [147/209] 481595

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