Huawei AR530 Series, Руководство по настройке

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Figure 6-6 Format of the Flags field
Bit7 Bit0
TCA （ Topology Change
Acknowledgment flag ）
TC （ Topology
Change flag ）
Reserved
TCN BPDU
A TCN BPDU contains only three fields: Protocol Identifier, Version, and Type, as shown in
Table 6-7 . The Type field is four bytes long and is fixed at 0x80.
When the network topology changes, TCN BPDUs are transmitted upstream until they reach
the root bridge. A TCN BPDU is generated in one of the following scenarios:
l A port transitions to the Forwarding state, and the local device has at least one designated
port.
l A designated port receives a TCN BPDU and sends a copy to the root bridge.
6.2.4 STP Topology Calculation
After STP is enabled on all devices on a network, all devices consider themselves the root bridge.
They only transmit and receive BPDUs and do not forward user traffic. All ports on the devices
are in Listening state. Then the devices select the root bridge, root ports, and designated ports
based on configuration BPDUs.
BPDU Exchange
Figure 6-7 shows the initial information exchange process. The four parameters in a pair of
brackets represent the root ID (S1_MAC and S2_MAC are BIDs of the two devices), root path
cost, sender BID, and PID. Configuration BPDUs are sent at Hello intervals.
Figure 6-7 Initial BPDU exchange
S1 S2
{S1_MAC,0,S1_MAC,A_PID}
{S2_MAC,0,S2_MAC,B_PID}
A
B
STP Algorithm Implementation
1. Initialization
Because each bridge considers itself the root bridge, the BPDU sent from a port is set as
follows:
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
6 STP/RSTP Configuration
Issue 01 (2014-11-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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