With the rapid development of the Internet, network-based applications gradually increase. This puts more and higher requirements for the reliability of the network. It is of course a good reliability solution for all network devices; however, in accordance with the perspective of protecting existing investments, it can be used to use cheap redundant ideas to find a balance in reliability and economy. Virtual routing redundancy protocol is a good solution. In this protocol, a redundant backup of the Default Gateway on the terminal IP device on the shared multi-access media (such as an Ethernet), so that the backup routing device is forwarded in time when one routing device is dowtry. Work, provide transparent switches to users, improve network service quality. 1. Overview of the protocol In a network based on TCP / IP protocol, in order to ensure communication between devices that do not directly physically connect, the route must be specified. There are two ways to currently specify the route: one is dynamic learning through routing protocols (such as: internal routing protocol RIP and OSPF); the other is a static configuration. Each terminal runs a dynamic routing protocol is unrealistic. Most of the client operating system platforms do not support dynamic routing protocols, even if support is also limited by monitoring, convergence, security, etc. Therefore, the static routing configuration of the terminal IP device is commonly used, which is generally specified to specify one or more default gateways to the terminal device. The static routing method simplifies the complexity of network management and the communication overhead of the terminal device, but it still has a disadvantage: if the router is damaged as the default gateway, all the communication to use the gateway will inevitably interrupt. Even if multiple default gateways are configured, if you do not restart the terminal device, you cannot switch to a new gateway. The Virtual Router Redundancy Protocol (VRRP) can be used very well to avoid static designation gateways. In the VRRP protocol, there are two groups of important concepts: VRRP routers and virtual routers, master routers, and backup routers. VRRP router refers to a router that runs VRRP, a physical entity, a virtual router refers to the VRRP protocol, which is a logical concept. A set of VRRP routers work together to constitute a virtual router. The virtual router is externally behaving as a logical router with a unique fixed IP address and a MAC address. The router in the same VRRP group has two mutual exclusive roles: master router and backup router, there is a router in a VRRP group and only one host role, there can be one or more routers in backup roles. . VRRP Protocol Use Select Policy from the router group as a master, responsible for ARP, and forwarding IP packets, and other routers in groups are standby in standby. When a main controller is fails, the backup router can upgrade to the primary router after a few seconds of time. Since this switching is very rapid and does not have to change the IP address and the MAC address, the terminal user system is transparent. Second, the working principle A VRRP router has the only ID: VRID, range is 0-255. The router performs an external virtual MAC address, the format of the address is 00-00-5e-00-01- [VRID]. The master router is responsible for answering the MAC address for the ARP request. In this way, no matter how to switch, it is guaranteed to the terminal device is the only consistent IP and MAC address, which reduces the impact of switching on the terminal device. VRRP control packets have only one: VRRP Notification (Advertisement). It uses IP multicast packets to encapsulate, and the group address is 224.0.0.0.18, and the publishing range is limited to the same LAN. This ensures that the VRID can be reused in different networks. In order to reduce network bandwidth consumption, only the master router can send VRRP advertisement packets.
