Router Election Rules - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

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Router Election Rules

If the master router becomes unavailable, the following rules govern election of the
master router:
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.
If the master router stops advertising for a predetermined period of time, the
remaining routers using the same VRID enter an election process to determine
which router takes over the master router responsibilities.
Depending on the configuration, the master router that does not own the IP
addresses might do one of the following:
Drop all packets that have destination addresses to these IP addresses
(default)
Accept packets that have destination addresses to these IP addresses as if
the addresses belonged to the master router (using the ip vrrp accept-data
command).
If the elected master router fails, backup routers start the election process again.
When the original master router becomes operational again, it restarts
broadcasting advertisements as long as preemption is enabled or the master
router is the address owner. Packet forwarding responsibility then shifts back
to the original master router.
The backup router assigned the highest priority for each VRID becomes the
master router.
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.
How VRRP Is Implemented in E Series Routers
Chapter 5: Configuring VRRP
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