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Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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Configuring Fast Hellos for Link State Detection

To achieve sub-second link-down detection so that convergence is triggered faster, use RSTP fast hellos.

The standard RSTP link-state detection mechanism does not offer the same low link-state detection speed.

RSTP fast hellos decrease the hello interval to the order of milliseconds and all timers derived from the hello timer are adjusted accordingly. This feature does not inter-operate with other vendors, and is available only for RSTP.

Configure a hello time on the order of milliseconds. PROTOCOL RSTP mode hello-time milli-second interval The range is from 50 to 950 milliseconds.

Example of Verifying Hello-Time Interval 

Dell(conf-rstp)#do show spanning-tree rstp brief
                                 Executing IEEE compatible Spanning Tree Protocol
                                 Root ID     Priority 0, Address 0001.e811.2233
                                 
                                 Root Bridge hello time 50 ms, max age 20, forward delay 15
                                 Bridge ID   Priority 0, Address 0001.e811.2233
                                 We are the root
                                 Configured hello time 50 ms, max age 20, forward delay 15
  • NOTE: The hello time is encoded in BPDUs in increments of 1/256ths of a second. The standard minimum hello time in seconds is 1 second, which is encoded as 256. Millisecond. hello times are encoded using values less than 256; the millisecond hello time equals (x/1000)*256. When you configure millisecond hellos, the default hello interval of 2 seconds is still used for edge ports; the millisecond hello interval is not used.

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