int fa0/0
standby 1 track 50 decrement 10
standby 1 track 51 decrement 10
track 50 rtr 50
track 51 rtr 50 reachability
rtr 50
type echo protocol ipIcmpEcho 1.1.1.1
request-data-size 100
timeout 1000
threshold 1000
frequency 2
rtr schedule 50 life forever start-time now
can anyone tell me what is the difference between the track 50,51 with and without reachability?
and what is the parameters timeout,frequency and threshold mean?