1. Overview of VRRP

• VirtualRouter Redundancy Protocol (VRRP)
• VRRP can virtualize multiple routers into a virtual router without changing the networking. By configuring the IP address of the virtual router as the default gateway, the backup of the gateway can be realized.
• Using VRRP, a group of routers (interfaces in the same LAN) work together, but only one is in the Master state, and the router (the interface) in this state undertakes the actual data traffic forwarding task.

2. Working principle of VRRP

(1) The routers in the virtual router elect the Master according to the priority.By sending gratuitous ARP packets, the master router notifies its own virtual MAC address to the devices or hosts connected to it, so as to undertake the task of packet forwarding;

(2) The Master router periodically sends VRRP packets to announce its configuration information (priority, etc.) and working status;

(3) If the Master router fails, the Backup router in the virtual router will re-elect a new Master according to the priority;
(4) When the virtual router state switches, the Master router switches from one device to anotherThe new master router simply sends a gratuitous ARP packet carrying the virtual router's MAC address and virtual IP address information, so that the ARP-related information in the host or device connected to it can be updated.The hosts on the network cannot perceive that the Master router has been switched to another device.
(5) When the priority of the Backup router is higher than that of the Master router, the working mode (preemptive and non-preemptive) of the Backup router determines whether to re-elect the Master.

3. VRRP active and standby backup process

(1) When the priority is set, the priority with the larger priority is the same, and the mac address of the interface is compared

(2) After the routers are configured, they do not know the configuration of the other side, and will send advertisement messages to each other to elect the active and standby routers

(3) Elect the active and standby routers

(4) After the master and backup are elected, the backup will not send messages

(5) The master always sends notification messages periodically

4. Experimental configuration

The first step: set the ip subnet mask and gateway of pc1, pc2, pc3

Step 2: Configure the port ip and subnet mask of the three routers

Step 3: Routers r2 and r3 use the vrrp protocol

Step 4: Configure the static routes of routers r1, r2, and r3

Step 5: Test

pc2 ping pc1

pc2 tracert pc1

The sixth step: disconnect the two lines of r2 and test again