VRRP implementation principle and basic functions of an S series switch

S series switches (S1700 excluded) support the VRRP function. Virtual Router Redundancy Protocol (VRRP) integrates multiple routing devices into a virtual routing device, and the IP address of the virtual routing device is used as the default gateway address to communicate with external networks. When the gateway is faulty, VRRP can select a new gateway to transmit data traffic, ensuring network reliability.

The working process of VRRP is as follows:

1. The VRRP group selects a new master based on the priorities of devices. The master sends gratuitous ARP packets to notify the connected network devices or hosts of the virtual MAC address of the VRRP group, and forwards packets to the virtual IP address.

2. The master periodically sends VRRP Advertisement packets to all backup devices in the VRRP group to advertise its configurations (such as the priority) and operating status.

3. If the master is faulty, VRRP elects a new master from the VRRP group based on priorities.

4. After a VRRP master/backup switchover, the new master sends gratuitous ARP packets carrying the virtual MAC address and virtual IP address of the virtual router to update the MAC address entry on the connected host or device. The user traffic is then switched to the new master.

5. If the original master recovers and is the IP address owner (its priority is 255), it immediately switches to the Master state. If the original device has a priority less than 255, it will switch to the Backup state first, and recover its priority to the previously configured priority before the faulty occurs.

6. If a backup router's priority is higher than the master router's priority, VRRP determines whether to re-elect a new master, depending on the backup router's working mode (preemption or non-preemption).

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