Concept Guide

Configuring Fast Hellos for Link State Detection
Use RSTP fast hellos to achieve sub-second link-down detection so that convergence is triggered faster. 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.
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.
822 Rapid Spanning Tree Protocol (RSTP)