Vrrp Configuration - D-Link xStack DGS-3610 Series Configuration Manual

DGS-3610 Series Configuration Guide
46
46.1 Overview
The Virtual Router Redundancy Protocol (VRRP) is designed to work in the active/standby
mode to ensure that the function switching can be implemented without affecting internal
and external data communication, and the internal network parameters need no modification.
Multiple devices within a VRRP group are mapped to a virtual device. The VRRP ensures
one and only one device to send packets on behalf of the virtual device at one time, while the
host sends packets to that virtual device. The device that forwards packets is elected as the
master device. If that device cannot work due to some cause, the one in standby status will
be selected to replace it and become the master device. The VRRP enables the host in the
LAN seems to use only one router and ensure the router connectivity even when the
currently-used first-hop router fails.
The RFC 2338 defines the IP packet format in VRRP type and its working mechanism. The
VRRP packets mean a kind of multicast packet with specified destination address, which are
sent by the master router in specified time to indicate its operation and are also used to elect
the master router. With VRRP, when the router undertaking route forwarding function in the
IP LAN fails, another router can automatically take over the operations, thus implementing
the hot-backup and error-tolerance of IP routing and ensuring the continuity and reliability of
host communication in the LAN. Redundancy is implemented for a VRRP application group
through multiple devices, but only one device acts as the master device at any time to
undertake the route forwarding function. The others are in the backup roles. The switching
between those devices in the VRRP application group is fully transparent for the host in the
LAN. The RFC 2338 defines the device switching rules:
1. The VRRP protocol adopts the preempt method to select the master device. First, it
compares the VRRP priorities that are set for the interfaces of the routers in a VRRP
group. The one with the highest priority becomes the master router and its status will
become Master. If the priority of the routers is identical, compare the master IP address
of the network interfaces, the one with larger IP address will become the master router
and the actual route service will be provided by it.
2. After the master device is elected, the others are in the backup status and monitor the
status of the master device through the VRRP packet sent by the master device. In
normal operation, the master device sends a VRRP packet at an interval, called
advertised packet, to notify the backup devices. The master device is in the normal
working status. If the backup device within the group does not receive the packet from
the master device for a long time, the status itself will be switched to the Master. If more
Chapter 46 VRRP Configuration

VRRP Configuration

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