1962 CHAPTER 106: BACKUP CENTER CONFIGURATIONn ■ When a dialer interface acts as the PPPoE client and the PPPoE session works inpermanent on-line mode, it can be configured as the main interface.■ When a BRI interface is used for the ISDN leased line, it can be configured asthe main interface.Backup interfaceBackup interfaces are those functioning as backups for main interfaces (Forexample, interfaces Serial 2/1 and Serial 2/2 in Figure 578), which are generallyidle. A backup interface can be any physical interface.n ■ One backup interface can only back up one main interface.■ One main interface can be configured up to three backup interfaces.■ Up to 10 main interfaces can be configured on a device at one time.How the Backup CenterWorksThe following is how the backup center works:Interface backupAs shown in Figure 579, interface Serial 2/0 on Router A acts as the main interfaceand interfaces Serial 2/1 and Serial 2/2 act as the backup interfaces.Figure 579 Diagram for main/backup modeIn interface backup mode, at any given time, only one interface takes on datatransmission.■ When the main interface is operating normally, even if the traffic is overloaded,the backup interface is in a backup state. All traffics are transmitted throughthe main interface.■ Only when the main interface cannot transmit data because of interfacefailure, the backup interface with a higher priority will take the main interfaceinstead and take on all traffic transmission.■ After the failed main interface restores, data transmission will be switched overto the main interface. At any given time, only one interface takes on datatransmission.Load sharingAs shown in Figure 580, interface Serial 2/0 on Router A acts as the maininterface, and interfaces Serial 2/1 and Serial 2/2 act as the backup interfaces.S2/1S2/0S2/2Router ARouter BLAN100%
