Planet XGS3-24042 User Manual download pdf (Page 589)

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65.1.2 VRRPv3 Working Mechanism

The working mechanism of VRRPv3 is the same with that of VRRPv2, which is mainly implemented via the

interaction of VRRP advertisement messages. It will be briefly described as follows:

Each VRRP router has a unique ID: VRIP, ranging from 1 to 255. This router has a unique virtual MAC

address outwardly, and the format of which is 00-00-5E-00-02-{VRID} (the format of virtual MAC address in

VRRPv2 is 00-00-5E-00-01-{VRID}). Master router is in charge of using this MAC address to respond to ND

neighbor request (it is ARP request in VRRPv2). Thus, no matter what switch is made, the terminal devices

will get the same IP and MAC address all the time, reducing the affection that the switch causes on terminal

devices.

There is only one kind of VRRP control message: VRRP advertisement. It uses IP multicast data packets to

encapsulate, and the format of multicast addresses is FF02:0:0:0:0:0:XXXX:XXXX. In order to keep a

consistence with the multicast address in VRRPv2 (224.0.0.18), the multicast addresses used by VRRPv3

advertisement messages can be FF02:0:0:0:0:0:0:12, and the advertisement is limited within the same LAN.

Thus, different VRID are guaranteed to be used repeatedly in different networks. In order to reduce the

overheads of network bandwidth, only master routers can send VRRP advertisement messages regularly.

Backup routers will start a new round of VRRP selection if it hasn’t received a VRRP advertisement in 3

advertisement intervals in a row or if it receives an advertisement with a priority of 0.

In a VRRP router group, the master router is selected according to priority. The range of priority in VRRP

protocol is 0-255. If the IP address of a VRRP router is the same to that of the virtual router interface, then the

virtual router will be called the IP address owner in the VRRP group; the IP address owner automatically has

the highest priority: 255. The priority of 0 is usually used when the IP address owner gives up the role of

master. The range of priority can be configured is 1-254. The configuration rule of priority can be set

according to the speed and cost of the link, the performance and reliability of the router and other

management policies. In the selection of the master router, the virtual router with high priority will win. So, if

there is an IP owner in the VRRP group, it will always be the master router. For the candidate routers having

the same priority, selection will be done according to the magnitude of IP addresses (the bigger IP address

takes precedence). VRRP also provides a preemptive priority policy. If such policy is configured, the backup

router with higher priority will preempt the role of new master router over the current master router with lower

priority.

In order to avoid the fault of returning a physical MAC address when Pinging virtual IP, it is regulated that

virtual IP can not be the real IP of the interface. Thus, all the interfaces participating of the backup group

selection will be backup by default.

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Planet XGS3-24042 User Manual Page 589

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