H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 15)

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You can adjust the interval for sending VRRP advertisements by setting the VRRP advertisement interval
timer. If a backup receives no advertisements in a period three times the interval, the backup regards itself
as the master and sends VRRP advertisements to start a new master election.
VRRP preemption delay timer
To avoid frequent state changes among members in a VRRP group and provide the backups enough time
to collect information (such as routing information), each backup waits for a period of time (the
preemption delay time) after it receives an advertisement with the priority lower than the local priority,
then sends VRRP advertisements to start a new master election in the VRRP group and becomes the
master.
Packet format
The master periodically multicasts VRRP packets to declare its presence. VRRP packets are also used for
checking the parameters of the virtual router and electing the master.
VRRP packets are encapsulated in IP packets, with the protocol number being 112.
Figure 3 shows the
format of a VRRPv2 packet.
Figure 3 Format of a VRRPv2 packet
A VRRP packet comprises the following fields:
• Version—Version number of the protocol: 2 for VRRPv2.
• Type—Type of the VRRPv2 packet. It must be VRRP advertisement, represented by 1.
• Virtual Rtr ID (VRID)—ID of the virtual router. 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 IPv4 addresses for the VRRP group. A VRRP group can have
multiple virtual IPv4 addresses.
• Auth Type—Authentication type. 0 means no authentication, 1 means simple text authentication,
and 2 means MD5 authentication.
• Adver Int—Interval for sending advertisement packets. For VRRPv2, the interval is in seconds and
defaults to 1.
• Checksum—16-bit checksum for validating the data in VRRP packets.
• IP Address—Virtual IPv4 address entry of the VRRP group. The Count IP Addrs field defines the
number of the virtual IP v4 addresses.
• Authentication Data—Authentication key. Currently, this field is used only for simple authentication
and is 0 for any other authentication mode.