Loop prevention and breaking on S series switch


For S series switches except S1700 switches, use any of the following methods to remove loops:
1. Configure features such as STP, RSTP, MSTP, VBST,RRPP, and SEP to prevent loops.
2. Bundle dual physical links into a single logical link to prevent loops while implementing redundancy and increasing bandwidth.
3. Configure the switch to transparently transmit packets of different VLANs along different paths.
4. Enable loop detection and loopback detection to detect loops on the switch or downstream network connected to the switch, and configure the switch to take the preconfigured action to remove loops. Fixed switches only support loopback detection.

Other related questions:
Unexpected breaking down of S series switch
If a switch stopping responding during operating, upgrade the switch or install the related patch. If the fault persists, collect diagnosis information and contact Huawei technical support at e_online@huawei.com.

How to select loop prevention protocols
When creating a new network using S series switches (except the S1700), select loop prevention protocols based on your network requirements:
1.   If the network services have high performance requirements (for example, if millisecond-level convergence is required when a fault occurs), select the SEP, RRPP, and SMLK protocols. Otherwise, select the STP protocol.
2.   If you are creating a ring network, select the SEP and RRPP protocols. If you are creating a tree network, select the STP protocol. If two uplink ports are used to transmit data, select the SMLK protocol.
3.   If the network must connect to other vendors' devices, select the STP protocol. Otherwise, select the Smart Ethernet Protection (SEP) protocol. SEP is a technology developed by Huawei that supports topology viewing, multiple modes for selecting blocking points, and millisecond-level fault convergence time. SEP is recommended for new networks.

Loop prevention mechanisms on CE series switches at the edge of a TRILL network
Currently, you can perform the following operations to detect and eliminate loops when user-side devices connect to a TRILL network: 1. Configure the assured forwarding (AF) function on the edge device of the TRILL network so that only one device forwards user traffic, preventing loops. 2. In V100R003C00 and later versions, configure association between TRILL and MSTP when an MSTP network connects to a TRILL network. 3. In V100R003C00 and V100R003C10, configure an E-Trunk to enable dual-homing access to TRILL for active-active access if user-side devices are servers or network devices are dual-homed to the TRILL network. 4. In V100R005C00 and later versions, configure a multi-chassis link aggregation group (M-LAG) to enable dual-homing access to TRILL for active-active access if user-side devices are servers or network devices are dual-homed to the TRILL network.

How can I check whether a loop exists on an S series switch
The simplest way to check the existence of a loop on an S series switch (except the S1700) is to check whether a MAC address flapping alarm exists on the switch. If the alarm exists, you can quickly locate the loop based on the information in the alarm. Run the display mac-address flapping record command to check whether MAC address flapping exists, or run the display trapbuffer command to check whether the alarm contains The mac-address has flap value or MAC move detected. For more information, visit Layer 2 Loop Troubleshooting.

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