一、在多层交换网络中实现默认网关路由器冗余
       1、代理ARP：主机使用ARP来确定前往远程目的地的下一跳的MAC地址，本地路由器使用其MAC地址来响应。（如果负责转发的路由器故障，主机需要等待ARP超时后，再学习到其他路由器的MAC）
       2、IRDP（interior gateway routing protocol）：ICMP的一种扩展，动态发现默认路由器的一种协议。很少用，发现故障慢。IRDP生命周期。

二、ＨＳＲＰ（hot standby routing protocol）的作用及原理
       HSRP是cisco私有协议，在多台路由器之间共享的虚拟MAC地址和虚拟IP地址以及一个通过多播协议对LAN接口和串行接口进行监控的进程组成。虚拟成一个路由器（网关）提供服务，此时，ＰＣ的网关设置为虚拟网关地址。

       1、HSRP组件
              一台活跃路由器（发hello、回应PC ARP请求）、一台备用路由器（发hello、监听）、一台虚拟路由器（PC网关）、其他HSRP成员路由器（监听）
2、工作：协议包每３秒发送一次，持续１０秒（３个周期）。HSRP被 UDP封装，端口号是1985。目标IP为224.0.0.2
3、虚拟MAC：0000.0c07.ac01 0000.0c厂商编号 07ac HSRP编号 01 组号，最多支持256个组（标识一个组）
4、HSRP状态
       Initial：初始状态，HSRP未全面动转，修改配置或接口启动进入此状态
       Learn：学习状态，不知道虚拟IP，未看到活跃路由器发hello。等待活跃路由器发hello。
       Listen：监听状态，知道虚拟IP。没有活动和备份路由器信息。（其他HSRP成员路由器都处于此状态）
       Speak：发方状态，定期发hello，参与选举活跃路由器选举。
       Standby：备用状态，下一任活跃路由器，定期发hello。
       Active：活跃状态，转发HSRP虚拟MAC地址和IP的数据包。定期发hello。

三、配置及查看
       1、单组HSRP配置（备份）
              Int vlan 2
              Ip address 192.168.1.10 255.255.255.0
              Standby 1 ip 192.168.1.1（配置虚拟IP，组号默认为0）
              Standby 1 priority 200（越高越好，默认为100）
              Standby 1 preemt（抢占，默认没有）
              Standby 1 track f0/1 110（跟踪上行端口，110降优先级）
              R(config-if)#standby 1 authentication ?（认证）
                    WORD Plain text authentication string（默认cisco，明文显示）
                    md5   Use MD5 authentication（md5加密）
                    text Plain text authentication
              R(config-if)#standby 1 timers ?（时间，hello和hold time）
                     <1-254> Hello interval in seconds
msec     Specify hello interval in milliseconds（毫秒）
              同一个组号可以有不同的IP（secondary）。仍由STP控制数据流。HSRP的主应该是STP的根。
       2、多组HSRP（负载）
              在同一子网内做多个虚拟网关，不同的PC网关设置不同。实现负载
              interface Ethernet0/0
ip address 11.11.1.1 255.255.255.0
standby 1 ip 11.11.1.10
standby 1 priority 150
standby 1 preempt
standby 1 track Ethernet0/1 60
standby 2 ip 11.11.1.20
standby 2 priority 90
standby 2 preempt
standby 2 track Ethernet0/1
end
       3、查看
              Show standby
              Show standby brief
R#debug standby ?
               errors   HSRP errors
events   HSRP events
packets HSRP packets
terse    Display limited range of HSRP errors, events and packets

 

三层交换机上实现HSRP

HSRP是一种Cisco专有协议，它通过在冗余网关之间共享协议和MAC地址，提供了不间断的IP路径冗余。该协议由在两台路由器之间共享的虚拟 MAC地址和虚拟IP地址以及一个通过多波协议对LAN接口和串行接口进行监控的进程组成。HSRP支持将多台路由器用作备用默认网关。

将SW1和SW2组成一个HSRP组，实现路由器的冗余，首先按拓扑图所示配置IP地址，使用一台交换机来模拟PC，用一以路由器模拟WEB，在SW1、SW2和WEB之间配置EIGRP协议： 
sw1(config-if)#interface fa0/8
sw1(config-if)#no switchport
sw1(config-if)#ip address 10.1.1.3 255.255.255.0
sw1(config-if)#no shutdown
sw1(config-if)#interface vlan 1
sw1(config-if)#ip address 10.1.2.3 255.255.255.0
sw1(config-if)#no shutdown
sw1(config-if)#exit
sw1(config)#ip routing
sw1(config)#router eigrp 100
sw1(config-router)#network 10.0.0.0
sw1(config-router)#no auto-summary

sw2(config)#interface fa0/7
sw2(config-if)#no switchport
sw2(config-if)#ip address 10.1.1.2 255.255.255.0
sw2(config-if)#no shutdown
sw2(config-if)#interface vlan 1
sw2(config-if)#ip address 10.1.2.2 255.255.255.0
sw2(config-if)#no shutdown
sw2(config-if)#exit
sw2(config)#ip routing
sw2(config)#router eigrp 100
sw2(config-router)#network 10.0.0.0
sw2(config-router)#no auto-summary

WEB(config)#interface fa0/1
WEB(config-if)#ip address 10.1.1.4 255.255.255.0
WEB(config-if)#no sh
WEB(config-if)#exit
WEB(config)#router eigrp 100
WEB(config-router)#network 10.0.0.0
WEB(config-router)#no auto-summary

PC(config)#interface vlan 1
PC(config-if)#ip address 10.1.2.100 255.255.255.0
PC(config-if)#no shutdown
PC(config-if)#exit
PC(config)#ip default-gateway 10.1.2.1

将PC的网关指向了10.1.2.1，这个地址将是HSRP组的虚拟IP地址，配置HSRP： 
sw1(config)#interface vlan 1
sw1(config-if)#standby ip 10.1.2.1
sw1(config-if)#standby preempt

sw2(config)#interface vlan 1
sw2(config-if)#standby ip 10.1.2.1
sw2(config-if)#standby preempt

HSRP应在接口上配置，配置时应指定虚拟IP地址，参数preempt可以帮助优先级比较高的路由器在故障恢复后重新成为活跃路由器。

查看HSRP信息： 
sw1#show standby
Vlan1 - Group 0
Local state is Active, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.728
Virtual IP address is 10.1.2.1 configured
Active router is local
Standby router is unknown
Virtual mac address is 0000.0c07.ac00
2 state changes, last state change 00:00:32
IP redundancy name is "hsrp-Vl1-0" (default)

sw2#show standby
Vlan1 - Group 0
Local state is Speak, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.032
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.3, priority 100 expires in 7.176
Standby router is unknown
0 state changes, last state change never
IP redundancy name is "hsrp-Vl1-0" (default)

可以发现两者在默认情况下优先级相同，由于SW1是先初始化的，所以成为了活跃路由器，而SW2是备份路由器。

      在PC上执行trace，查看路由情况： 
PC#trace 10.1.1.4
Type escape sequence to abort.
Tracing the route to 10.1.1.4
1 10.1.2.3 0 msec 4 msec 0 msec
2 10.1.1.4 0 msec 4 msec *

可以看见，数据包是通过目前的活跃路由器SW1转发的。

如果将SW1与PC之间的链路断开，可以发现PC仍然能与WEB通讯，再次使用trace： 
PC#ping 10.1.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms
PC#trace 10.1.1.4
Type escape sequence to abort.
Tracing the route to 10.1.1.4
1 *
10.1.2.2 0 msec 0 msec
2 10.1.1.4 4 msec 0 msec *

可以看到路径改为通过SW2，而在SW1和SW2上查看HSRP信息： 
sw1#show standby
Vlan1 - Group 0
Local state is Init (interface down), priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Virtual IP address is 10.1.2.1 configured
Active router is unknown
Standby router is unknown
3 state changes, last state change 00:01:39
IP redundancy name is "hsrp-Vl1-0" (default)

sw2#show standby
Vlan1 - Group 0
Local state is Active, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.954
Virtual IP address is 10.1.2.1 configured
Active router is local
Standby router is Unknown
Virtual mac address is 0000.0c07.ac00
2 state changes, last state change 00:01:07
IP redundancy name is "hsrp-Vl1-0" (default)

可以看到此时SW1的状态是阻塞，而SW2成为了活跃路由器。

将SW1与PC之间的链路恢复，再次查看SW1的HSRP信息： 
sw1#show standby
Vlan1 - Group 0
Local state is Listen, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.2, priority 100 expires in 9.448
Standby router is unknown
3 state changes, last state change 00:02:03
IP redundancy name is "hsrp-Vl1-0" (default)

sw1#show standby
Vlan1 - Group 0
Local state is Speak, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.996
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.2, priority 100 expires in 9.164
Standby router is unknown
3 state changes, last state change 00:02:12
IP redundancy name is "hsrp-Vl1-0" (default)

sw1#show standby
Vlan1 - Group 0
Local state is Standby, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.528
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.2, priority 100 expires in 7.384
Standby router is local
4 state changes, last state change 00:00:01
IP redundancy name is "hsrp-Vl1-0" (default)

可以看到SW1经过了监听、发言之后，最终成为了备份路由器。由于SW1和SW2都采用的是默认的优先级100，即使我们配置了抢占（preempt）选项，SW1也无法重新成为活跃路由器。此时，我们可以手工指定SW1的优先级：
sw1(config)#interface vlan 1
sw1(config-if)#standby priority 150
00:23:25: %STANDBY-6-STATECHANGE: Vlan1 Group 0 state Standby -> Active
sw1#show standby
Vlan1 - Group 0
Local state is Active, priority 150, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.252
Virtual IP address is 10.1.2.1 configured
Active router is local
Standby router is unknown
Virtual mac address is 0000.0c07.ac00
5 state changes, last state change 00:00:03
IP redundancy name is "hsrp-Vl1-0" (default)

可以看到SW1重新成为了活跃路由器。

此时，如果我们断开SW1与WEB之间的链路： 
sw1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
     10.0.0.0/24 is subnetted, 2 subnets
C     10.1.2.0 is directly connected, Vlan1
D     10.1.1.0 [90/28416] via 10.1.2.2, 00:01:49, Vlan1
sw1#show standby
Vlan1 - Group 0
Local state is Active, priority 150, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.728
Virtual IP address is 10.1.2.1 configured
Active router is local
Standby router is unknown
Virtual mac address is 0000.0c07.ac00
2 state changes, last state change 00:00:32
IP redundancy name is "hsrp-Vl1-0" (default)

PC#trace 10.1.1.4
Type escape sequence to abort.
Tracing the route to 10.1.1.4
1 10.1.2.3 4 msec 0 msec 4 msec
2 10.1.2.2 0 msec 0 msec 4 msec
3 10.1.1.4 4 msec 0 msec *

此时，SW1仍然保持它活跃路由器的身份，但是从SW1并不能直接到达WEB，流量会通过SW2转发，这样就带来了性能问题，可以通过配置track参数来解决这个问题。

      将WEB与SW1恢复连通，配置track参数： 
sw1(config)#interface vlan 1
sw1(config-if)#standby track fa0/8 51

这表示当Fa0/8出现问题时，SW1的优先级将自动减少51，这样能保证此时SW1的优先级比SW2更低，而让SW2成为活跃路由器。

      再次断开SW1与WEB之间的连接： 
sw1#show standby
Vlan1 - Group 0
Local state is Standby, priority 99 (confgd 150), may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.674
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.2, priority 100 expires in 7.516
Standby router is local
4 state changes, last state change 00:00:07
IP redundancy name is "hsrp-Vl1-0" (default)
Priority tracking 1 interface or object, 0 up:
Interface or object       Decrement     State
FastEthernet0/8                51             Down (administratively down)

可以看到此时SW1的优先级变成了99，成为了备份路由器。

HSRP工作过程中，HSRP组中始终只有一台路由器处在转发状态，这无疑对资源造成了极大的浪费。我们可以能过配置多个HSRP组，对不同的HSRP组指定不同的活跃路由器，将主机的网关指向不同的虚拟IP地址，以达到负载均衡的目的。

      删除之前的HSRP操作，创建两个HSRP组： 
sw1(config)#interface vlan 1
sw1(config-if)#no standby ip 10.1.2.1
sw1(config-if)#standby 1 ip 10.1.2.1
sw1(config-if)#standby 1 preempt
sw1(config-if)#standby 1 track fa0/8
sw1(config-if)#standby 2 ip 10.1.2.254
sw1(config-if)#standby 2 preempt
sw1(config-if)#standby 2 priority 95
sw1(config-if)#standby 2 track fa0/8

sw2(config)#interface vlan 1
sw2(config-if)#no standby ip 10.1.2.1
sw2(config-if)#standby 1 ip 10.1.2.1
sw2(config-if)#standby 1 preempt
sw2(config-if)#standby 1 track fa0/7
sw2(config-if)#standby 1 priority 95
sw2(config-if)#standby 2 ip 10.1.2.254
sw2(config-if)#standby 2 preempt

我们对SW1和SW2的不同HSRP组分别配置了不同的优先级，保证他们在不同的组里处于不同的角色，实现了负载均衡： 
sw1#show standby
Vlan1 - Group 1
Local state is Active, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.210
Virtual IP address is 10.1.2.1 configured
Active router is local
Standby router is unknown
Virtual mac address is 0000.0c07.ac01
5 state changes, last state change 00:00:06
IP redundancy name is "hsrp-Vl1-1" (default)
Priority tracking 1 interface or object, 1 up:
Interface or object          Decrement     State
FastEthernet0/8                    10               Up
Vlan1 - Group 2
Local state is Standby, priority 95, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.346
Virtual IP address is 10.1.2.254 configured
Active router is 10.1.2.2, priority 100 expires in 7.680
Standby router is local
4 state changes, last state change 00:01:22
IP redundancy name is "hsrp-Vl1-2" (default)
Priority tracking 1 interface or object, 1 up:
Interface or object          Decrement     State
FastEthernet0/8                    10               Up

sw2#show standby
Vlan1 - Group 1
Local state is Standby, priority 95, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.384
Virtual IP address is 10.1.2.1 configured
Active router is 10.1.2.3, priority 100 expires in 9.872
Standby router is local
3 state changes, last state change 00:02:48
IP redundancy name is "hsrp-Vl1-1" (default)
Priority tracking 1 interface or object, 1 up:
Interface or object          Decrement     State
FastEthernet0/7                    10               Up
Vlan1 - Group 2
Local state is Active, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 1.358
Virtual IP address is 10.1.2.254 configured
Active router is local
Standby router is 10.1.2.3 expires in 7.908
Virtual mac address is 0000.0c07.ac02
1 state changes, last state change 00:04:24
IP redundancy name is "hsrp-Vl1-2" (default)
Priority tracking 1 interface or object, 1 up:
Interface or object          Decrement     State
FastEthernet0/7                    10               Up

在PC上使用trace命令： 
PC#trace 10.1.1.4
Type escape sequence to abort.
Tracing the route to 10.1.1.4
1 10.1.2.3 4 msec 0 msec 4 msec
2 10.1.1.4 4 msec 0 msec *

将PC的默认网关改为10.1.2.254，再次trace： 
PC(config)#ip default-gateway 10.1.2.254
PC(config)#end
PC#trace 10.1.1.4
Type escape sequence to abort.
Tracing the route to 10.1.1.4
1 10.1.2.2 1000 msec 0 msec 4 msec
2 10.1.1.4 4 msec 0 msec *

可以看到PC在两种情况下使用了不同的路由器来转发数据，实现了负载均衡的目的。

热备份HSRP配置

 

r1(config)#int f0/0
r1(config-if)#ip add 192.168.1.1 255.255.255.0
r1(config-if)#no shu
r1(config-if)#int f1/0
r1(config-if)#ip add 192.168.2.1 255.255.255.0
r1(config-if)#no shu
r1(config)#router rip
r1(config-router)#network 192.168.1.0 
r1(config-router)#network 192.168.2.0
r1(config)#int f0/0
r1(config-if)#standby 47 ip 192.168.1.254    备份组为47虚拟IP为1.254
r1(config-if)#standby 47 priority 180        优先级为180
r1(config-if)#standby 47 preemtp             配置占先权
r1(config-if)#standby 47 track f1/0 100      端口跟踪，优先级减少100
r2(config)#int f0/0r2(config-if)#ip add 192.168.1.2 255.255.255.0
r2(config-if)#no shu
r2(config-if)#int f1/0
r2(config-if)#ip add 192.168.3.1 255.255.255.0
r2(config-if)#no shu
r2(config)#router rip
r2(config-router)#network 192.168.1.0 
r2(config-router)#network 192.168.3.0
r2(config)#int f0/0
r2(config-if)#standby 47 ip 192.168.1.254    备份组为47虚拟IP为1.254
r2(config-if)#standby 47 priority 150        优先级为150
r3(config)#int f0/0
r3(config-if)#ip add 192.168.2.2 255.255.255.0
r3(config-if)#no shu
r3(config-if)#int f1/0
r3(config-if)#ip add 192.168.3.2 255.255.255.0
r3(config-if)#no shu
r3(config-if)#int f2/0
r3(config-if)#ip add 192.168.4.1 255.255.255.0
r3(config-if)#no shu
r3(config)#router rip 
r3(config-router)#network 192.168.2.0
r3(config-router)#network 192.168.3.0
r3(config-router)#network 192.168.4.0
VPCS1:ip 192.168.1.3 192.168.1.254 24        VPCS1IP为1.3网关为1.254
VPCS2:ip 192.168.4.2 192.168.4.1 24          VPCS2IP为4.2网关为4.1
之后测试就可以了。