H3C Technologies H3C S12500-X Series Switches - Manual (Page 77)

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Device Comparison process
Configuration BPDU on
ports after comparison
Device C
• Port C1 receives the configuration BPDU of Port A2 {0, 0,
0, Port A2}, finds that the received configuration BPDU is
superior to its existing configuration BPDU {2, 0, 2, Port
C1}, and updates its configuration BPDU.
• Port C2 receives the original configuration BPDU of Port
B2 {1, 0, 1, Port B2}, finds that the received configuration
BPDU is superior to the existing configuration BPDU {2, 0,
2, Port C2}, and updates its configuration BPDU.
• Port C1: {0, 0, 0, Port
A2}
• Port C2: {1, 0, 1, Port
B2}
• Device C compares the configuration BPDUs of all its
ports, decides that the configuration BPDU of Port C1 is
the optimum, and selects Port C1 as the root port with the
configuration BPDU unchanged.
• Based on the configuration BPDU and path cost of the root
port, Device C calculates the configuration BPDU of Port
C2 {0, 10, 2, Port C2}, and compares it with the existing
configuration BPDU of Port C2 {1, 0, 1, Port B2}. Device C
finds that the calculated configuration BPDU is superior to
the existing one, selects Port C2 as the designated port,
and replaces the configuration BPDU of Port C2 with the
calculated one.
• Root port (Port C1): {0,
0, 0, Port A2}
• Designated port (Port
C2): {0, 10, 2, Port C2}
• Port C2 receives the updated configuration BPDU of Port
B2 {0, 5, 1, Port B2}, finds that the received configuration
BPDU is superior to its existing configuration BPDU {0, 10,
2, Port C2}, and updates its configuration BPDU.
• Port C1 receives a periodic configuration BPDU {0, 0, 0,
Port A2} from Port A2, finds that it is the same as the
existing configuration BPDU, and discards the received
one.
• Port C1: {0, 0, 0, Port
A2}
• Port C2: {0, 5, 1, Port
B2}
• Device C finds that the root path cost of Port C1 (10) (root
path cost of the received configuration BPDU (0) plus path
cost of Port C1 (10)) is larger than that of Port C2 (9) (root
path cost of the received configuration BPDU (5) plus path
cost of Port C2 (4)), decides that the configuration BPDU of
Port C2 is the optimum, and selects Port C2 as the root
port with the configuration BPDU unchanged.
• Based on the configuration BPDU and path cost of the root
port, Device C calculates a designated port configuration
BPDU for Port C1 {0, 9, 2, Port C1} and compares it with
the existing configuration BPDU of Port C1 {0, 0, 0, Port
A2}. Device C finds that the existing configuration BPDU is
superior to the calculated one and blocks Port C1 with the
configuration BPDU unchanged. Then Port C1 does not
forward data until a new event triggers a spanning tree
calculation process, for example, the link between Device
B and Device C is down.
• Blocked port (Port C1):
{0, 0, 0, Port A2}
• Root port (Port C2): {0,
5, 1, Port B2}
After the comparison processes described in Table 7 , a spanning tree with Device A as the root bridge
is established, and the topology is shown in Figure 17 .