1-2Figure 1-1 LAN networkingHost 1EthernetSwitchNetworkHost 2 Host 310.100.10.7/24 10.100.10.9/2410.100.10.8/2410.100.10.1/24The networking illustrated in Figure 1-1 requires high stability of the default gateway. Normally, addingegress gateways is used to improve the system reliability. In this case, how to route between multipleegresses needs to be solved.Virtual Router Redundancy Protocol (VRRP), an error-tolerant protocol defined in RFC 2338, wellsolves the problem mentioned above through separating physical devices and logical devices. In LANswith multicast or broadcast capabilities (such as Ethernet), VRRP can avoid single point failure throughestablishing backup links without modifying the configuration of dynamic routing protocols and routerdiscovery protocols.Introduction to VRRP GroupVRRP allows you to combine a group of LAN switches (including a master and several backups) into aVRRP group. The VRRP group functions as a virtual router, forwarding packets as a gateway.Figure 1-2 VRRP network diagramHost 1EthernetMasterNetworkHost 2 Host 3Backup10.100.10.7/24 10.100.10.9/2410.100.10.8/24Actual IP address10.100.10.2/24Actual IP address10.100.10.3/24Virtual IP address10.100.10.1/24Virtual IP address10.100.10.1/24As shown in Figure 1-2, a VRRP group has the following features:z The virtual router (the VRRP group) has its own IP address (10.100.10.1 in the above figure).z The switches within the VRRP group must have their own IP addresses (such as 10.100.10.2 forthe master and 10.100.10.3 for the backup).z Hosts in the LAN use the IP address of the virtual router (that is, 10.100.10.1) as their defaultgateway.
