Industry Cellular Gateway
2.9 Redundancy
In engineering, redundancy is the duplication of critical components or functions of a system with the
intention of increasing reliability of the system, usually in the form of a backup or fail-safe. In an IP networking,
the access gateway is the critical part of the networking system. Redundant gateway plays the backup one of
the master gateway and it will take over the data transmitting job once it finds the master gateway failed.
The purchased gateway can serve as the redundant gateway of core router in the enterprise by using the
Virtual Router Redundancy Protocol (VRRP).
2.9.1 VRRP
Virtual Router Redundancy Protocol (VRRP) is a computer networking protocol providing device redundancy.
It allows a backup router or switch to automatically take over if the primary (master) router or switch fails.
This increases the availability and reliability of routing paths via automatic default gateway selections on an IP
network.
The protocol achieves this by creation of virtual routers, which are an abstract representation of multiple
routers, i.e. master and backup routers, acting as a group. The default gateway of a participating host is
assigned to the virtual router instead of a physical router. If the physical router that is routing packets on
behalf of the virtual router fails, another physical router is selected to automatically replace it. The physical
router that is forwarding packets at any given time is called the master router.
A group of physical VRRP gateways combined together to play a virtual server with one unique virtual server
ID and one unique virtual server IP address. But these VRRP gateways have their own priority values to serve
as the sequence for backing up the master gateway.
The gateway with VRRP function can join one group of redundant gateways to serve as the backup one for the
master gateway. Fill same values of virtual server ID and IP for these gateways, and each gateway owns its
own priority as the sequence in the backup list. They construct a VRRP redundant gateway group. Following
diagram illustrates the group example with two member gateways.
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