Format Of Vrrp Packets - H3C S5500-EI Series Operation Manual

Operation Manual – VRRP
H3C S5500-EI Series Ethernet Switches
You can adjust the interval of sending VRRP advertisements by setting the VRRP
advertisement interval timer. If a backup switch receives no advertisements in three
times the interval, the backup switch regards itself as the master switch and sends
VRRP advertisements to start a new master switch election.
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
0
Version
Auth Type
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.
3 7
Type Virtual Rtr ID
Adver Int
Figure 1-3, an IPv4-based VRRP packet consists of the following fields:
15
Priority
IP address 1
IP address n
Authentication data 1
Authentication data 2
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Chapter 1 VRRP Configuration
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Count IP Addrs
Checksum
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