Introduction to VRRP 1975Format of VRRP Packets VRRP uses multicast packets. The router acting as the master sends VRRP packetsperiodically to declare its existence. VRRP packets are also used for checking theparameters of the virtual router and electing the master.IPv4-based VRRP packet formatFigure 585 IPv4-based VRRP packet formatAs shown in Figure 585, an IPv4-based VRRP packet consists of the followingfields:■ Version: Version number of the protocol, 2 for VRRPv2.■ Type: Type of the VRRP packet. Only one VRRP packet type is present, that is,VRRP advertisement, which is represented by 1.■ Virtual Rtr ID (VRID): Number of the virtual router, that is, number of thestandby group. It ranges from 1 to 255.■ Priority: Priority of the router in the standby group, in the range 0 to 255. Agreater value represents a higher priority.■ Count IP Addrs: Number of virtual IP addresses for the standby group. Astandby group can have multiple virtual IP addresses.■ Auth Type: Authentication type. 0 means no authentication, 1 means simpleauthentication, and 2 means MD5 authentication.■ Adver Int: Interval for sending advertisement packets, in seconds. The default is1.■ Checksum: 16-bit checksum for validating the data in VRRP packets.■ IP Address: Virtual IP address entry of the standby group. The allowed numberis given by the Count IP Addrs field.■ Authentication Data: Authentication key. Currently, this field is used only forsimple authentication and is 0 for any other authentication modes....Version Type Virtual Rtr ID Priority Count IP AddrsAuth Type Adver Int ChecksumIP address 1IP address nAuthentication data 1Authentication data 20 7 15 23 313
