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Default route provides convenience for user’s configuration operations but also imposes high
requirements on stability of the default gateway device. Increasing exit gateway is a common
method for improving system reliability. Then, the problem to be solved is how to select route
among multiple exits.
VRRP (Virtual Router Redundancy Protocol) adds a set of routers that can undertake gateway
function into a backup group to form a virtual router. The election mechanism of VRRP will decide
which router to undertake the forwarding task and the host in LAN is only required to configure the
default gateway for the virtual router.
VRRP is a fault-tolerant protocol. It improves reliability, while simplifying the host’s configuration.
In the LAN with multicast or broadcast capability (e.g. Ethernet), the default link with high
reliability can be provided relying on VRRP in case of fault with a router, which can effectively
avoid network interruption in case of fault with a single link without the need to modify the
dynamic routing protocol, router discovery protocol and other configuration information.
8.3.2 Brief Introduction of Virtual Router ID
VRRP will bring together a set of routers in LAN. It consists of multiple routers and is similar to a
virtual router in respect of function. According to the vlan interface ip of different network
segments, it can be virtualized into multiple virtual routers. Each virtual router has an ID number
and up to 255 can be virtualized.
VRRP has the following characteristics:
• Virtual router has an IP address, known as the Virtual IP address. For the host in LAN, it is only
required to know the IP address of virtual router, and set it as the address of the next hop of the
default route.
• Host in the network communicates with the external network through this virtual router.
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