The principle of virtual Router Redundancy protocol: VRRP

Why to use VRRP technology

We know that in order to achieve device communication between different subnets, routing needs to be configured. There are two common ways to specify routing:

The first is through routing protocols: RIP, OSPF dynamic learning

The second way is through static routing: Configuring a static route for a terminal pc.

Each of these two routes has its own advantages and disadvantages:

The first route can automatically find the optimal path, and neighbor routing can learn to get the routing table, but dynamic routing takes up the line bandwidth and CPU processing time.

The second route is not required CPU processing time also does not occupy the line bandwidth, but this route needs to the terminal PC configuration gateway to achieve, the workload is relatively large.

Both of these routes are now widely used.

We are now only going to analyze the drawbacks of static routing, because the VRRP technology is used on static routes, not on dynamic routes.

For static routing, configure the default gateway for the terminal PC. If the router that is the default gateway fails, all communication to the host that uses the gateway for the next hop is interrupted. As shown in the following figure;

In the figure above, host A- D are configured with a default gateway: 10.1.1.1, the next hop in Gateway routing points to a router in the network segment where the host is located Routera,routera sends the message to the extranet, but if Routera is broken now, all hosts will not be able to communicate with the other network segments.

To solve the above problem, we can add a router routerb, as shown in the following illustration:

When Routera broke down, all the PCs switched network concerns to gateways on the Routerb. This enables the router to be backed up. This technology is VRRP technology---virtual router Redundancy protocol

VRRP Introduction (Forwarding mechanism)

1. VRRP (Virtual Router redundancy Protocol) will be able to assume the gateway function of the router to join the backup group, the formation of a virtual router, by the VRRP election mechanism to determine which routers assume the forwarding task, The host within the LAN simply configures the virtual router as the default gateway

2. VRRP is a fault-tolerant protocol that simplifies the configuration of hosts while improving reliability. In a LAN with multicast or broadcast capability, such as Ethernet, VRRP can still provide a high reliable default link when a device fails, effectively avoiding the problem of network interruption after single link failure without modifying configuration information such as dynamic routing protocol, routing Discovery Protocol, etc.

3. The implementation of the VRRP protocol has VRRPV2 and VRRPv3 two versions, VRRPv2 Ipv4,vrrpv3 based on IPV6

4. VRRP routers: All routers running the VRRP protocol are called VRRP routers

5. VRRP Backup group: Multiple routers are divided into one group, in which a primary router is elected and the other is a backup router. Usually the main router is a work, backup routers idle, when the main router failure, from multiple backup routers to elect a replacement for the fault of the main router. The routers in this group form a backup group.

As shown in the following illustration: There are two routers, two gateways, from two routers to elect a router as the main router, the other is the backup router, the primary router is responsible for forwarding datagrams, and the backup router is idle, when the main router fails, the backup router becomes the main router, The forwarding function is implemented in lieu of the main router.