VRRP协议简述
VRRP（虚拟路由冗余协议）：通过把几台路由设备联合组成一台虚拟路由设备，将虚拟路由设备的IP地址作为用户的默认网关地址实现与外部的通讯。当网关设备发生故障时，VRRP协议能够快速选举新的网关设备承担数据流量，保障网络的可靠通信。
Master路由器的选举：首先比较每台路由器的优先级，优先级大的成为Master路由器，优先级相同的话，就比较接口IP地址，IP地址大的成为Master路由器。Master路由器会周期性的发送Advertisement报文（组播），如果Backup路由器在规定的间隔时间内没收到Master路由器发来的Advertisement报文，则认为Master路由器“挂掉”了，那么就会进行新一轮的选举。
VRRP的三种状态：Initialize、Master和Backup
VRRP有三种状态：Initialize , Master, Backup
- Initialize 状态：
系统刚启动VRRP的状态；在此状态，不处理VRRP报文。- Master状态：
当路由器处于Master状态时，路由器会处理：
1、每隔1s发送VRRP组播报文，来报告自己的状态。
2、响应对虚拟IP地址的ARP请求，并且响应的是虚拟MAC地址，而不是接口的真实MAC地址。
3、转发目的MAC是虚拟MAC的IP报文。
4、如果是虚拟IP拥有者，接受目的IP地址是虚拟IP地址的报文，否则丢弃。
5、当接受到优先级大的VRRP报文时，变成backup；接口shutdown后，变为initialize状态。- Backup状态：
当路由器处于backup状态时，路由器将：
1、监听Master发送的VRRP报文，如果在3个周期内不能接受到，变为master，并发送免费ARP（为什么）。
2、不响应对虚拟IP地址的ARP请求。
3、丢弃目的MAC为虚拟MAC的IP报文。
4、丢弃目的IP为虚拟IP地址的报文。
拓扑图（含IP规划）
配置任务
按照拓扑图要求配置IP地址，配置VRRP虚拟路由冗余协议（将R1的eth0/0/0、R2的eth0/0/0加入到vrrid 1中并设置好优先级选择R1作为主用路由器、将R1的eth0/0/1、R2的eth0/0/1加入到vrrid 2中并设置好优先级选择R2作为主用路由器），并最终实现PC1和PC3的互相通信，且PC1->PC3所使用的网关设备是R1，PC3->PC1所使用的网关设备是R2。配置工具
华为网络设备仿真平台eNSP
VRRP虚拟路由冗余协议的配置
配置步骤（含完整指令）
首先，配置主机PC1、PC2、PC3的IP信息很简单（注意，我们这里准备配置VRRP协议，所以这个网关地址就填那个“虚拟”的IP地址），比如PC1就这样：
配置主机PC1
然后，需要配置的是R1、R2的各个端口所分配的IP地址，以R1为例，需要配置的有Eth0/0/0（192.168.1.2/24）、Eth0/0/1（192.168.2.2/24）端口。
<Huawei>sys #R1
Enter system view, return user view with Ctrl+Z.
[Huawei]int eth0/0/1
[Huawei-Ethernet0/0/1]ip address 192.168.2.2 24
[Huawei-Ethernet0/0/1]
Jul 26 2019 15:47:40-08:00 Huawei %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP on the interface Ethernet0/0/1 has entered the UP state.
Jul 26 2019 15:47:42-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 1, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]int eth0/0/0
[Huawei-Ethernet0/0/0]ip address 192.168.1.2 24
[Huawei-Ethernet0/0/0]
Jul 26 2019 15:50:59-08:00 Huawei %%01IFNET/4/LINK_STATE(l)[1]:The line protocol IP on the interface Ethernet0/0/0 has entered the UP state.
Jul 26 2019 15:51:02-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 2, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]
<Huawei>sys #R2
Enter system view, return user view with Ctrl+Z.
[Huawei]int eth0/0/0
[Huawei-Ethernet0/0/0]ip address 192.168.1.3 24
[Huawei-Ethernet0/0/0]
Jul 26 2019 15:51:50-08:00 Huawei %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP on the interface Ethernet0/0/0 has entered the UP state.
Jul 26 2019 15:51:52-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 1, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]int eth0/0/1
[Huawei-Ethernet0/0/1]ip address 192.168.2.3 24
[Huawei-Ethernet0/0/1]
Jul 26 2019 15:52:05-08:00 Huawei %%01IFNET/4/LINK_STATE(l)[1]:The line protocol IP on the interface Ethernet0/0/1 has entered the UP state.
Jul 26 2019 15:52:12-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 2, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]
再然后，就具体在路由器上配置vrrp协议：
[Huawei]int eth0/0/0 #R1
[Huawei-Ethernet0/0/0]vrrp vrid 1 virtual-ip 192.168.1.254
[Huawei-Ethernet0/0/0]
Jul 26 2019 16:19:10-08:00 Huawei %%01VRRP/4/STATEWARNINGEXTEND(l)[4]:Virtual Router state BACKUP changed to MASTER, because of protocol timer expired. (Interface=Ethernet0/0/0, VrId=1, InetType=IPv4)
Jul 26 2019 16:19:13-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 10, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]vrrp vrid 1 priority 120 #设置优先级（默认优先级为100，所以120这个就会在选举中成为主用路由）
[Huawei-Ethernet0/0/0]
Jul 26 2019 16:19:33-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 11, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]vrrp vrid 1 preempt-mode ?
disable Cancel current configuration
timer Specify timer
[Huawei-Ethernet0/0/0]vrrp vrid 1 preempt-mode timer delay 20 #设置抢占等待时间
[Huawei-Ethernet0/0/0]
Jul 26 2019 16:20:23-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 12, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]vrrp vrid 1 track interface eth0/0/1 reduced 30 # 监控上层端口状态调整优先级
[Huawei-Ethernet0/0/0]
Jul 26 2019 16:20:53-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 13, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]int eth0/0/1
[Huawei-Ethernet0/0/1]vrrp vrid 2 virtual-ip 192.168.2.254
[Huawei-Ethernet0/0/1]
Jul 26 2019 16:24:13-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 14, the change loop count is 0, and the maximum number of records is 4095.
Jul 26 2019 16:24:15-08:00 Huawei %%01VRRP/4/STATEWARNINGEXTEND(l)[5]:Virtual Router state BACKUP changed to MASTER, because of protocol timer expired. (Interface=Ethernet0/0/1, VrId=2, InetType=IPv4)
[Huawei-Ethernet0/0/1]
针对这条指令
vrrp vrid 1 preempt-mode timer delay 20 #设置抢占等待时间举个例子，R1的Eth0/0/0地址192.168.1.2/24 和 R2的Eth0/0/0地址192.168.1.3/24作为下层PC1的待选择网关，根据我们上面的拓扑图设置，R1的Eth0/0/0地址192.168.1.2/24会被选举为Master状态，也就是说下层PC1、PC2的网关地址会是192.168.1.2/24。
假设我们的R1因为故障宕机了，那么下层的PC1、PC2的网关地址岂不是会出错？当然了，VRRP自然不会容忍这种情况，即VRRP机制会让处于Master状态的R1不断地向所有处于Backup状态的R2间隔性发生VRRP组播报文，这样在R1宕机或是出现其他故障问题后，R2就会发现在一段时间内它都无法收到R1的VRRP组播报文，这样它就会认为R1已经“离开”了，然后发起新一轮的“选举”。
那么，这里的抢占等待时间，也就是说，R1在20s内没有发送VRRP组播报文（即R2在20s内没有收到VRRP组播报文），才会发起新的“选举”。（默认这个延迟等待时间是0s）
试想一下，我们这里为什么不推荐直接采用默认配置（0s）呢？
再来谈谈这条指令
vrrp vrid 1 track interface eth0/0/1 reduced 30 # 监控上层端口状态调整优先级!
分析这种情况
上面图中很明显地，标明VRRP协议所“选举”出来的Master状态的R1的上层链路出现故障，这时候，R1的Eth0/0/0端口的IP地址就不能再担当下层PC1、PC2的网关IP地址了，这在本拓扑图中很明显吧。VRRP协议有这样的规定——我可以监控R1的所有（或特定的某个）上层端口（可以理解为“非网关”端口），每当我探查到其中一个出现链路故障，我就给这个参与“选举”的R1降低优先级。
试想一下，我们为什么不对出现上层链路不通的路由器直接做“剥夺选举资格”的操作？
[Huawei]int eth0/0/0 #R2
[Huawei-Ethernet0/0/0]vrrp vrid 1 virtual-ip 192.168.1.254
[Huawei-Ethernet0/0/0]
Jul 26 2019 16:27:53-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 3, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/0]int eth0/0/1
[Huawei-Ethernet0/0/1]vrrp vrid 2 virtual-ip 192.168.2.254
[Huawei-Ethernet0/0/1]
Jul 26 2019 16:28:33-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 4, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]vrrp vrid 2 priority 120
[Huawei-Ethernet0/0/1]
Jul 26 2019 16:28:45-08:00 Huawei %%01VRRP/4/STATEWARNINGEXTEND(l)[0]:Virtual Router state BACKUP changed to MASTER, because of priority calculation. (Interface=Ethernet0/0/1, VrId=2, InetType=IPv4)
Jul 26 2019 16:28:53-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 5, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]vrrp vrid 2 preempt-mode timer delay 20
[Huawei-Ethernet0/0/1]
Jul 26 2019 16:29:13-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 6, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]vrrp vrid 2 track interface eth0/0/0 reduced 30
[Huawei-Ethernet0/0/1]
Jul 26 2019 16:29:43-08:00 Huawei DS/4/DATASYNC_CFGCHANGE:OID 1.3.6.1.4.1.2011.5.25.191.3.1 configurations have been changed. The current change number is 7, the change loop count is 0, and the maximum number of records is 4095.
[Huawei-Ethernet0/0/1]
结果验证
- ping验证（PC1上ping PC3）
PC>ping 192.168.2.1
Ping 192.168.2.1: 32 data bytes, Press Ctrl_C to break
From 192.168.2.1: bytes=32 seq=1 ttl=127 time=187 ms
From 192.168.2.1: bytes=32 seq=2 ttl=127 time=78 ms
From 192.168.2.1: bytes=32 seq=3 ttl=127 time=94 ms
From 192.168.2.1: bytes=32 seq=4 ttl=127 time=78 ms
From 192.168.2.1: bytes=32 seq=5 ttl=127 time=94 ms
--- 192.168.2.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 78/106/187 ms
- tracert验证
PC>tracert 192.168.2.1 #PC1->PC3的路由追踪
-
YI7
';]=`
traceroute to 192.168.2.1, 8 hops max
(ICMP), press Ctrl+C to stop
1 192.168.1.2 78 ms 47 ms 46 ms
2 192.168.2.1 94 ms 78 ms 94 ms
PC>tracert 192.168.1.4 #PC3->PC1的路由追踪
traceroute to 192.168.1.4, 8 hops max
(ICMP), press Ctrl+C to stop
1 192.168.2.3 78 ms 47 ms 47 ms
2 192.168.1.4 78 ms 94 ms 93 ms
VRRP与BFD
当R1或R1到R2间链路出现故障时，VRRP报文“重新选举”需要一定的协商周期。为了实现链路故障时快速切换，在链路中部署了BFD链路检测机制，实现当主用接口或者链路出现故障时，Backup状态设备迅速切换为Master状态，承担网络流量，以减少故障对业务传输的影响。
BFD：(Bidirectional Forwarding Detection，双向转发检测)协议提供一种轻负载、快速检测两台邻接路由器/交换机之间转发路径连通状态的方法，它是一个简单的“Hello”协议，在很多方面，它与那些著名的路由协议的邻居检测部分相似。之所以被称为双向，是因为BFD协议通过三次握手机制，能提供链路来回两个方向的连通性检测。
