RA#
interface Ethernet0
ip address 171.16.6.5 255.255.255.0
standby 1 ip 171.16.6.100
standby 1 priority 105 (Priority 值大，Active)
standby 1 preempt (int 0 down-> up，搶回 Active)
standby 1 track Serial0 (int down => Priority -10 => standby)
RB#
interface Ethernet0
ip address 171.16.6.6 255.255.255.0
standby 1 ip 171.16.6.100 (可不設，自動學習)
standby 1 preempt
standby 1 track Serial1
