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Example: Basic VRRP Configuration
Copyright © 2010, Juniper Networks, Inc.
If two backup routers were assigned the same priority, the router that has the highest
primary address becomes the master router. For example, if several routers were all
assigned the default priority of 100, the IP addresses must be compared.
Router election on a VRRP router can also be determined by whether the preemption
option is enabled.
When a backup router detects a master router with a lower priority than the backup
router has, the backup router might leave the current master router alone or take over
the current master router and become the master router itself.
When preemption is enabled, a backup router always preempts or takes over the
responsibility of the master router. When preemption is disabled, the lower-priority
backup is left in the master state.
NOTE: Using VRRP can override the source address of the ICMP redirect.
When a backup VRID functions as a master router on a given IP interface,
its ICMP redirects must fake the source IP address of the IP address owner.
The redirect must fake the IP address because hosts accept only an ICMP
redirect that is sent by the current gateway of the host.
VRRP Implementation in E Series Routers on page 152
Before You Configure VRRP on page 156
Configuring VRRP on page 157
As Figure 6 on page 154 shows, the basic VRRP configuration uses a single VRID (VRID 1).
Because R1 is the address owner, it serves as the master router. Router R2 is the backup
router. The four end hosts on subnet 1 are configured to use 10.0.0.1/8 as the default
router. IP address 10.0.0.1 is associated with VRID 1.
In this example, if R1 becomes unavailable, R2 takes over VRID 1 and its associated IP
addresses. Packets sent to IP destinations outside the 10.x.x.x subnet using 10.0.0.1 as
the router are then forwarded by R2. Even though R2 assumes R1's forwarding
responsibilities, it may or may not process any packet with destination address (DA)
10.0.0.1, depending on the accept-data configuration. When R1 becomes active again, it
takes over as the master router and R2 reverts to the backup router.
The VRRP MAC address is always 00-00-5e-00-01-vrid. The valid VRID range is
0x01–0xFF.
Chapter 6: Configuring VRRP
153
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