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.
776 Rapid Spanning Tree Protocol (RSTP)