Precautions for STP interworking on an S series switch

S (except the S1700) series switches adopt the standard STP/RSTP/MSTP algorithm. When a Huawei switch that runs STP interworks with a non-Huawei device, pay attention to the following:
1. If the non-Huawei device runs the standard STP algorithm, the Huawei switch can interwork properly with the device.
2. If the non-Huawei device runs a non-standard STP protocol except the Cisco Per VLAN Spanning Tree (PVST) protocol, the Huawei switch can transparently transmit STP packets from the device after the stp disable and bpdu enable commands are executed on the interface of the Huawei device connected to the non-Huawei device.
3. If the non-Huawei device is a Cisco device that runs PVST, the Huawei switch cannot negotiate with the device, but can transparently transmit packets from the device.
4. Check whether the configurations (such as the mode, root priority, and path cost) between the non-Huawei device and Huawei switch are consistent with each other.
5. Check the Proposal/Agreement mechanism. In enhanced mode, the current interface calculates the root interface when calculating the synchronization flag bit. In common mode, the interface ignores the root interface when calculating the synchronization flag bit.
You can run the stp no-agreement-check command to configure the common fast transition mechanism on an interface. By default, the enhanced fast transition mechanism is configured on an interface.
6. There are two formats of MSTP BPDUs. One is dot1s, the format regulated in IEEE802.1s; the other is legacy, a private BPDU format. If the format of MSTP BDPUs is set to dotls on one interface and legacy on the peer interface, the negotiation fails. You can run the stp compliance { auto | dot1s | legacy } command to configure the specified STP BDPU format. The auto mode is set to allow an interface to automatically use the format of MSTP BDPUs sent from the remote interface. In this manner, the two interfaces use the same MSTP BDPU format. By default, MSTP BDPUs use the auto mode.
7. When a Huawei device is connected to a non-Huawei device, if the region name, revision level, and VLAN-to-instance mapping configured on the two devices are the same but the BPDU keys are different, the two devices cannot communicate with each other. To address this problem, run the stp config-digest-snoop command to enable the digest snooping function so that the BPDU keys on Huawei and non-Huawei devices are consistent.

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