R3166-R3206-HP High-End Firewalls High Availability Configuration Guide-6PW101

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VRRP preemption delay timer
In an unstable network, a backup can fail to receive the packets from the master due to network
congestion and thus the members in the group change their states frequently. Set the VRRP preemption
delay timer to address the problem.
With the VRRP preemption delay timer set, if a backup receives no advertisement in a period three times
the advertisement interval and then the preemption delay, it considers that the master fails. In this case,
the backup regards itself as the master and sends VRRP advertisements to start a new master election in
the VRRP group.
Format of VRRP packets
VRRP uses multicast packets. The router acting as the master sends VRRP packets periodically to declare
its existence. VRRP packets are also used for checking the parameters of the virtual router and electing
the master.
Figure 3 Format of IPv4-based VRRP packet
As shown in Figure 3, an IPv4-based VRRP packet consists of the following fields:
• 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): Serial number of the virtual router, that is, serial number of the VRRP group. It
ranges from 1 to 255.
• Priority: Priority of the router in the VRRP group, in the range 0 to 255. A greater value represents
a higher priority.
• Count IP Addrs: Number of virtual IP addresses for the VRRP group. A VRRP group can have
multiple virtual IP addresses.
• Auth Type: Authentication type. 0 means no authentication, 1 means simple text authentication,
and 2 means MD5 authentication.
• Adver Int: Interval for sending advertisements, in seconds. The default is 1.
• Checksum: 16-bit checksum for validating the data in VRRP packets.
• IP Address: Virtual IP address entry of the VRRP group. The Count IP Addrs field defines the number
of the virtual IP addresses.
• Authentication Data: Authentication key. This field is used only for simple authentication and is 0 for
any other authentication modes.