Enabling STP/RSTP
Context
Before enabling STP/RSTP, ensure that you have performed all basic configurations, such as the device priority and port priority, on the device and its ports. After STP/RSTP is enabled on a ring network, spanning tree calculation starts immediately on the network. Making changes to configurations will affect spanning tree calculation and may cause network flapping.
Procedure
- Run system-view
The system view is displayed.
STP/RSTP-enabled devices calculate spanning trees by exchanging BPDUs. Therefore, all the ports participating in spanning tree calculation must be enabled to send BPDUs to the CPU for processing. By default, a port is enabled to send BPDUs to the CPU. You can run the bpdu enable command in the interface view to enable a port to send BPDUs to the CPU. The S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S do not support the bpdu command.
- Run stp enable
STP/RSTP is enabled on the device.
By default, STP/RSTP is enabled on a device. If you specify a VLANIF interface of a VLAN as the management network interface for an STP/RSTP-enabled device, you can run the ethernet-loop-protection ignored-vlan command to specify this VLAN as an ignored VLAN. Then interfaces in the ignored VLAN will not enter the Blocking state and stay in Forwarding state. Therefore, services will not be interrupted on these interfaces.
To prevent the CPU from being affected and faults such as network flapping from occurring, the following lists the recommended maximum number of STP-enabled ports in Up state for different models:
S2720-EI, S5720-LI, S5735-L, S5735S-L, S5735S-L-M, S5720S-LI, S5730-SI, S5730S-EI, S6720-LI, S6720S-LI, S6720-SI, S6720S-SI, S5720I-SI, S5720-SI, S5735-S, S5735S-S, S5735-S-I, and S5720S-SI: 128
S5720-EI: 200
S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S: 256
Follow-up Procedure
When the topology of a spanning tree changes, the forwarding paths for associated VLANs are changed. Devices need to update the ARP entries corresponding to those VLANs. Depending on how devices process ARP entries, STP/RSTP convergence mode can be fast or normal.
In fast mode, ARP entries to be updated are directly deleted.
In normal mode, ARP entries to be updated are rapidly aged.
The remaining lifetime of ARP entries to be updated is set to 0 to immediately age the ARP entries out. If the number of ARP aging probes is greater than 0, the device performs aging probe for these ARP entries.
Run the stp converge { fast | normal } command in the system view to configure the STP/RSTP convergence mode.
By default, the normal STP/RSTP convergence mode is used. The normal mode is recommended. If the fast mode is used, ARP entries will be frequently deleted, causing a high CPU usage (even 100%). As a result, network flapping will frequently occur.