使用Standby Preempt和Standby Track命令

简介

本文档介绍standby preempt和standby track命令如何协同工作以及如何使用。

先决条件

要求

本文档没有任何特定的要求。

使用的组件

本文档中的信息基于以下软件版本：

• 运行Cisco IOS®软^件版本12.2(10b)的路由器

本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您的网络处于活动状态，请确保您了解所有命令的潜在影响。

规则

有关文档规则的详细信息，请参阅Cisco技术提示规则。

背景信息

standby preemptcommand使具有最高优先级的热备份路由器协议(HSRP)路由器立即成为活动路由器。优先级的确定首先取决于所配置的优先级值，然后取决于 IP 地址。在每种情形下，都是更高的值具有更高的优先级。当一个更高优先级的路由器优先于一个较低优先级的路由器时，该路由器会发送一条 Coup 消息。当优先级较低的活动路由器从一个更高优先级的活动路由器接收到 Coup 消息或 Hello 消息时，该路由器会更改为对话状态，并发送放弃消息。

standby trackcommand允许您在路由器上指定另一个接口，供HSRP进程进行监控，以便更改给定组的HSRP优先级。如果指定接口的线路协议关闭，则会降低 HSRP 优先级。这意味着，如果另一台优先级较高的HSRP路由器启用了备用抢占，则该路由器可以成为活动路由器。

下图显示了一个将standby preemptcommand与standby trackcommand结合使用的示例。

备用抢占和备用跟踪配置

配置示例

在网络图中，HSRP 是以这种方式配置的：

• R1是活动路由器，跟踪R1 Serial 0接口状态。当R1是活动路由器时，从主机（主机1、主机2、主机3）到服务器的所有流量都通过R1路由。

• R2是备用路由器并跟踪R2 Serial 1接口状态。

• 如果R1 Serial 0接口关闭，则R1 HSRP优先级会减少10。此时，R2 HSRP优先级高于R1,R2将接管活动路由器的角色。

• 当R2成为活动路由器时，从主机到服务器的所有流量都会通过R2路由。

注：主机1、2和3的默认网关配置了HSRP虚拟IP地址（本例中为172.16.6.100）。在路由器上配置一个路由协议（例如 RIP），可实现主机和服务器之间的连接。

这是每台路由器的配置：

interface Ethernet0 
 ip address 172.16.6.5 255.255.255.0

!--- Assigns an IP address to the interface.

 no ip redirects 
 standby 1 ip 172.16.6.100

!--- Assigns a standby group and standby IP address

 standby 1 priority 105

!--- Assign a priority (105 in this case) to the router interface (e0) 
!--- for a particular group number (1). The default is 100.

 standby 1 preempt

!--- Allows the router to become the active router when the priority 
!--- is higher than all other HSRP-configured routers in the hot standby group. 
!--- If you do not use the standby preempt command in the configuration 
!--- for a router, that router does not become the active router, even if 
!--- the priority is higher than all other routers. 

 standby 1 track Serial0

!--- Indicates that HSRP tracks Serial0 interface. 
!--- The interface priority can also be configured, which indicates the 
!--- amount by which the router priority decreases when 
!--- the interface goes down. The default is 10.

interface Serial0 
 ip address 172.16.2.5 255.255.255.0

interface Ethernet0
 ip address 172.16.6.6 255.255.255.0

!--- Assigns an IP address to the interface.

 no ip redirects
 standby 1 ip

!--- Indicates the hot standby group. Here the IP address of the virtual 

router !--- is not configured. See the note after this table.

standby 1 preempt

!--- Allows the router to become the active router when the priority 
!--- is higher than all other HSRP-configured routers in the hot standby group. 
!--- If you do not use the standby preempt command in the configuration 
!--- for a router, that router does not become the active router, even if 
!--- the priority is higher than all other routers. 

standby 1 track Serial1

!--- Indicates that HSRP tracks Serial1 interface. 
!--- The interface priority can also be configured, which indicates the 
!--- amount by which the router priority decreases when 
!--- the interface goes down. The default is 10. 
!--- The priority is also not configured and hence the default 
!--- priority value of 100 is applied.

interface Serial1
 ip address 172.16.7.6 255.255.255.0

注意：R2未配置备用IP地址。这样做是特意为了显示出这是有效配置。当 R1 和 R2 交换 HSRP hello 时，R2 从 R1 获知备用 IP 地址。为R2配置备用IP地址（在R1上配置相同的备用地址）也是有效配置。

R1#show standby
Ethernet0 - Group 1
Local state is Active, priority 105, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.458
Virtual IP address is 172.16.6.100 configured
Active router is local
Standby router is 172.16.6.6 expires in 8.428
Virtual mac address is 0000.0c07.ac01
2 state changes, last state change 02:09:49
IP redundancy name is "hsrp-Et0-1" (default)
Priority tracking 1 interface, 1 up:
Interface    Decrement  State
Serial0         10      Up
 
R2#show standby
Ethernet0 - Group 1
Local state is Standby, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.814
Virtual IP address is 172.16.6.100
Active router is 172.16.6.5, priority 105 expires in 9.896
Standby router is local
3 state changes, last state change 00:10:21
IP redundancy name is "hsrp-Et0-1" (default)
Priority tracking 1 interface, 1 up:
Interface   Decrement  State
Serial1        10      Up

虽然 R2 没有配置 HSRP 优先级，但是输出显示 R2 优先级为 HSRP 默认值，即 100。两台路由器的输出都表明路由器跟踪串行接口的状态。R1 的状态是活动的，而 R2 的状态为备用。最后，两个路由器均使用 standby preempt 命令配置。

如果 R1 的 serial 0 接口断开，将会如何？show standby 命令的输出如下所示：

R1#show standby
Ethernet0 - Group 1
Local state is Standby, priority 95 (confgd 105), may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.670
Virtual IP address is 172.16.6.100 configured
Active router is 172.16.6.6, priority 100 expires in 8.596
Standby router is local
4 state changes, last state change 00:01:45
IP redundancy name is "hsrp-Et0-1" (default)
Priority tracking 1 interface, 0 up:
Interface    Decrement  State
Serial0         10      Down
   
R2#show standby
Ethernet0 - Group 1
Local state is Active, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.810
Virtual IP address is 172.16.6.100
Active router is local
Standby router is 172.16.6.5 expires in 9.028
Virtual mac address is 0000.0c07.ac01
4 state changes, last state change 00:01:38
IP redundancy name is "hsrp-Et0-1" (default)
Priority tracking 1 interface, 1 up:
Interface   Decrement  State
Serial1        10      Up

请注意，在输出中，R1的HSRP优先级降低了10到95。此更改使 R2 的优先级（其值为 100）高于 R1。当R2的优先级变高时，R2被配置为standby preempt，因此R2成为活动路由器，R1成为备用路由器。此时，如果 R1 serial 0 接口恢复，则 R1 优先级会重新变为 105。在这种情况下，R1 会抢占优先并再次成为 HSRP 活动路由器。

注意：如果R2上未配置standby preempt,R2不会向R1发送Coup消息，这会导致R2变为活动状态。这样的话，R1 将仍为活动路由器。

例如，请看以下配置：

standby priority 120
standby track serial 0
standby track serial 1

使用 standby priority命令配置HSRP优先级120，并配置HSRP以跟踪两个接口（Serial0和Serial1）的状态。由于 standby track 命令中指定递减值，则当所跟踪的接口断开时，HSRP 优先级以默认值 10 递减。最初，两个接口均启用，并且接口的 HSRP 优先级为 120，正如 show standby 命令输出中所示：

R1#show standby
Ethernet0 - Group 1
  Local state is Active, priority 120, may preempt
  Hellotime 3 sec, holdtime 10 sec
  Next hello sent in 1.034
  Virtual IP address is 10.0.0.5 configured
  Active router is local
  Standby router is unknown
  Virtual mac address is 0000.0c07.ac01
  2 state changes, last state change 00:00:04
  IP redundancy name is "hsrp-Et0-1" (default)
  Priority tracking 2 interfaces, 2 up:
    Interface                  Decrement  State
    Serial0                       10      Up
    Serial1                       10      Up

此时，接口 Serial 0 断开。

R1#
1w0d: %LINK-3-UPDOWN: Interface Serial0, changed state to down
1w0d: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to down
R1#

这会将HSRP优先级从120减少10到值110。可以使用 show standby 命令来验证：

R1#show standby
Ethernet0 - Group 1
  Local state is Active, priority 110 (confgd 120), may preempt
  Hellotime 3 sec, holdtime 10 sec
  Next hello sent in 2.544
  Virtual IP address is 10.0.0.5 configured
  Active router is local
  Standby router is unknown
  Virtual mac address is 0000.0c07.ac01
  2 state changes, last state change 00:00:48
  IP redundancy name is "hsrp-Et0-1" (default)
  Priority tracking 2 interfaces, 1 up:
    Interface                  Decrement  State
    Serial0                       10      Down  (line protocol down)
    Serial1                       10      Up

接下来，第二个所跟踪的接口 Serial 1 断开：

R1#
1w0d: %LINK-3-UPDOWN: Interface Serial1, changed state to down
1w0d: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down
R1#

这再次将HSRP优先级从110降低到100。可以使用 show standby 命令来验证：

R1#show standby
Ethernet0 - Group 1
  Local state is Active, priority 100 (confgd 120), may preempt
  Hellotime 3 sec, holdtime 10 sec
  Next hello sent in 1.846
  Virtual IP address is 10.0.0.5 configured
  Active router is local
  Standby router is unknown
  Virtual mac address is 0000.0c07.ac01
  2 state changes, last state change 00:01:06
  IP redundancy name is "hsrp-Et0-1" (default)
  Priority tracking 2 interfaces, 0 up:
    Interface                  Decrement  State
    Serial0                       10      Down  (line protocol down)
    Serial1                       10      Down  (line protocol down)

当任何一个所跟踪的串行接口（serial 0 或 serial 1）断开时，均导致优先级变为 110。当这两个所跟踪的串行接口（serial 0 和 serial 1）都断开时，导致优先级变为 100。

相关信息

• HSRP 支持页
• 技术支持和文档 - Cisco Systems