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400 C
HAPTER
17: V
IRTUAL
R
OUTER
R
EDUNDANCY
P
ROTOCOL
(VRRP)
Figure 45 Simple VRRP Configuration
In the example shown in Figure 45, Router A is the default gateway for
the workstation labeled PC, which provides access to the Wide Area
Network (WAN) and to the device labeled Server. Assume that no router
discovery protocols have been configured and that the default gateway is
static.
If the workstation loses its connection to Router A, the workstation loses
all remote connectivity because its default gateway is no longer available.
However, if VRRP is enabled in this same scenario, Router B detects the
loss of connectivity to Router A, and Router B assumes all forwarding
responsibilities on behalf of Router A. This transfer of forwarding
responsibilities allows the workstation to have continued access across
the WAN to the server.
Key Concepts
This section contains some VRRP definitions that you should know before
reading further.
■
VRRP router — A router running the VRRP protocol. A VRRP router
can:
■
Act as a Master router with actual addresses on a interface.
■
Act simultaneously as a Backup for other routers with additional
virtual router mappings and priorities for those routers.
■
Virtual router — A logical entity, managed by VRRP, that acts as the
default router for hosts on a shared LAN. The virtual router has a
unique identifier called the Virtual Router Identifier (VRID), and has a
set of associated IP addresses across the LAN.
Router A
Router B
WAN
PC
Router C
Router D
Server
L3
L3
L3
L3