HSRP一般用于两台，也可以用于多台。必须在每台起HSRP上的路由器上配置。
When the HSRP is configured on a network segment, it provides a virtual Media Access Control (MAC) address and an IP address that is shared among routers in a groupof routers that is running HSRP. One of these devices is selected by the protocol to be the active router. The active router receives and routes packets destined for the group's MAC address. For n routers running HSRP, there are n + 1 IP and MAC addresses assigned.
但是aceive只有一台，standby只有一台，其实其他的都在监听状态。所以zyx说的是处在active和standby的状态的只有两台。
附一个配置实例：
version 12.0
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname r1
!
enable password cisco
!
ip subnet-zero
!
!
!
!
interface Ethernet0
ip address 136.147.107.101 255.255.0.0
no ip redirects
no ip directed-broadcast
standby 150 timers 5 15 /* 定义150组5秒交换一次hello信息，15秒没收到
hello信息就开始切换 */
standby 150 priority 110 /* 定义150组的主路由器权值，值越大，为主路由
器希望越大 */
standby 150 preempt /* enable 150组的hsrp抢占功能 */
standby 150 authentication cisco /* 设置150组的router身份验证串 */
standby 150 ip 136.147.107.100 /* 定义150组的浮动地址，也是这台router
连接的网络的网关 */
standby 150 track Ethernet0 /* 定义监控的端口 */
!
interface Serial0
no ip address
no ip directed-broadcast
no ip mroute-cache
shutdown
no fair-queue
!
ip classless
!
!
line con 0
transport input none
line 1 16
line aux 0
line vty 0 4
password cisco
login
!
end