TP-Link JetStream T2700G-28TQ User Manual page 225

The VRRP priority ranges from 0 to 255 (the bigger the number is, the higher the priority is).
Configurable range is 1-254. The priority value 0 is reserved for the current master when it
gives up its role as master router. For example, when master router receives shutdown
message, it would send VRRP packet with priority 0 to the backup group which the interface
belongs to. The priority of the IP address owner must be 255. Therefore, if there exists an IP
address owner in the backup group and it works normally, it must be the master router.
3. State Transition
VRRP defines three state modes: Initialize, Master and Backup. Only in Master state can
master router provide service for forwarding request via virtual IP address and forward VRRP
packet.
When the system just starts, it comes to Initialize state. If the virtual router is not given a virtual
IP address, the system would maintain Initialize state. If the virtual IP address is configured
properly, when the system receives startup message from interface, it would transition to the
Backup state (in which case its priority is not 255) or Master state (in which case its priority is
255). Routers in master or backup state can change to Initialize state only when they receive
shutdown message from interface. In Initialize state, router cannot deal with VRRP packet.
If the master router functions properly, it will periodically send VRRP packets informing backup
routers in the backup group that it functions properly.
configured to customize the intervals that master router sends VRRP packet. If the backup
router waits for a period longer than three times the advertisement timer and fails to receive
VRRP packets from the master router, they will assume that the master router is dead and
initiate an election process by transitioning to the Master state and forwarding VRRP packets.
To avoid frequent Master-Backup state transition among routers in the backup group and
provide enough time for backup routers to collect necessary information, backup router would
not preempt to be master as soon as it receives packets with lower priority value. It would wait
for a certain time, which is called preempt-mode delay time, and then send packets to take
place of the former master. Users can customize the preempt-mode delay time.
4. Authentication Methods
VRRP provides three authentication methods:
No authentication: the eligibility of VRRP packets is not verified and no security insurance
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is provided. In a safe network, no authentication can be set as authentication method.
Simple text password: in a network where security is possible to be threatened, simple text
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password is recommended. The router which forwards the VRRP packets fills the
authentication data in the VRRP packets. The router which has received the VRRP
packets compares the data with that in local configuration. If they are the same, the VRRP
packet received is considered legitimate. If not, it would be considered as illegitimacy.
MD5 authentication: in a highly-unsecured network, MD5 authentication is recommended.
•
The router which sends the VRRP packets conducts digest operation on VRRP packets
using authentication data and MD5 algorithm. The result is saved in Authentication Header.
The router which has received the VRRP packet conducts the same digest operation and
compares the result with the content in Authentication Header. If they match, the VRRP
packet received is considered legitimate. If not, it would be considered as illegitimacy.
Interface Tracking
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This function enhances the backup function. If interface tracking is enabled, when the master
router's other interfaces which are not in this backup group (for example, the uplink interface)
fail, it would lower its priority value automatically. Therefore, router with more available
VRRP timer can be manually
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