Format Of Vrrp Packets - H3C S7500E Series Operation Manual

Operation Manual – HA
H3C S7500E Series Ethernet Switches
II. VRRP preemption delay timer
In an unstable network, a backup switch may fail to receive the packets from the master
switch due to network congestion, thus causing the members in the group to change
their states frequently. This problem can be addressed through setting the VRRP
preemption delay timer.
With the VRRP preemption delay timer set, if a backup switch receives no
advertisement in three times the advertisement interval and then in preemption delay, it
considers that the master fails. In this case, it regards itself as the master and sends
VRRP advertisements to start a new master switch election in a standby group.

1.1.4 Format of VRRP Packets

VRRP uses multicast packets. The switch 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.
I. IPv4-based VRRP packet format
Figure 1-3 IPv4-based VRRP packet format
As shown in
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 the standby
group. It ranges from 1 to 255.
Priority: Priority of the switch in the standby group, in the range 0 to 255. A greater
value represents a higher priority.
Count IP Addrs: Number of virtual IP addresses for the standby group. A standby
group can have multiple virtual IP addresses.
Auth Type: Authentication type. 0 means no authentication, 1 means simple
authentication, and 2 means MD5 authentication.
Adver Int: Interval for sending advertisement packets, in seconds. The default is 1.
Checksum: 16-bit checksum for validating the data in VRRP packets.
Figure 1-3, an IPv4-based VRRP packet consists of the following fields:
1-5
Chapter 1 VRRP Configuration