Zyxel OLT2412 [221/326] Vrrp overview

Zyxel OLT2412 [221/326] Vrrp overview
OLT2412 User’s Guide 221
CHAPTER 30
VRRP
This chapter shows you how to configure and monitor the Virtual Router Redundancy Protocol
(VRRP) on the OLT.
30.1 VRRP Overview
Each host on a network is configured to send packets to a statically configured default gateway
(this OLT). The default gateway can become a single point of failure. Virtual Router Redundancy
Protocol (VRRP), defined in RFC 2338, allows you to create redundant backup gateways to ensure
that the default gateway of a host is always available.
In VRRP, a virtual router (VR) represents a number of physical layer-3 devices. An IP address is
associated with the virtual router. A layer-3 device having the same IP address is the preferred
master router while the other Layer-3 devices are the backup routers. The master router forwards
traffic for the virtual router. When the master router becomes unavailable, a backup router assumes
the role of the master router until the master router comes back up and takes over.
The following figure shows a VRRP network example with the switches (A and B) implementing one
virtual router VR1 to ensure the link between the host X and the uplink gateway G. Host X is
configured to use VR1 (192.168.1.20) as the default gateway. If switch A has a higher priority, it is
the master router. Switch B, having a lower priority, is the backup router.
Figure 58 VRRP: Example 1
If switch A (the master router) is unavailable, switch B takes over. Traffic is then processed by
switch B.
172.21.1.1
172.21.1.1
172.21.1.100

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