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Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

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Sample RSTP configuration

The following is a sample of an RSTP configuration:

Configure RSTP on VLT peers to prevent forwarding loops—VLT peer 1 (primary)

Using the example shown in the Overview section as a sample VLT topology, the primary VLT switch sends BPDUs to an access device (switch or server) with its own RSTP bridge ID. BPDUs generated by an RSTP-enabled access device are only processed by the primary VLT switch. The secondary VLT switch tunnels the BPDUs that it receives to the primary VLT switch over the VLT interconnect. Only the primary VLT switch determines the RSTP roles and states on VLT ports and ensures that the VLT interconnect link is never blocked.

In the case of a primary VLT switch failure, the secondary switch starts sending BPDUs with its own bridge ID and inherits all the port states from the last synchronization with the primary switch. An access device never detects the change in primary/secondary roles and does not see it as a topology change.

The following examples show the RSTP configuration that you must perform on each peer switch to prevent forwarding loops.

Dell_VLTpeer1(conf)#protocol spanning-tree rstp
Dell_VLTpeer1(conf-rstp)#no disable
Dell_VLTpeer1(conf-rstp)#bridge-priority 4096
Dell_VLTpeer2(conf)#protocol spanning-tree rstp
Dell_VLTpeer2(conf-rstp)#no disable
Dell_VLTpeer2(conf-rstp)#bridge-priority 8192
NOTE When you remove the VLT configuration, RSTP is recommended as a backup solution to avoid spanning—tree loops. In this case, you can use the following RSTP default values:
  • hello–time: 2 seconds
  • forward–delay: 15 seconds
  • max–age: 20

There is no additional performance gain on VLT, if you configure the RSTP values other than the default values.

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