Configuring Passive Arp Learning For Backup Vrrp Routers - Juniper EX9200 Features Manual

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Configuring Passive ARP Learning for Backup VRRP Routers

Copyright © 2017, Juniper Networks, Inc.
For example, configure a VRRP group, vrrp-group1, with an advertise interval of 1 second,
startup silent period of 10 seconds, and an interface interface1 with a priority less than
255.
When interface1 transitions from down to up:
The vrrp-group1 group moves to the backup state, and starts the Master Down Event
timer (3 seconds; three times the value of the advertise interval, which is 1 second in
this case).
If no VRRP PDU is received during the 3-second period, the
seconds in this case) is checked, and if the startup silent period has not expired, the
Master Down Event timer is restarted. This is repeated until the
expires. In this example, the Master Down Event timer runs four times (12 seconds) by
the time the 10-second startup silent period expires.
If no VRRP PDU is received by the end of the fourth 3-second cycle, vrrp-group1 takes
over mastership.
Understanding VRRP on page 119
startup-silent-period on page 278
By default, the backup VRRP router drops ARP requests for the VRRP-IP to VRRP-MAC
address translation. This means that the backup router does not learn the ARP (IP-to-MAC
address) mappings for the hosts sending the requests. When it detects a failure of the
master router and transitions to become the new master router, the backup router must
re-learn all the entries that were present in the ARP cache of the master router. In
environments with many directly attached hosts, such as metro Ethernet environments,
the number of ARP entries to learn can be high. This can cause a significant transition
delay, during which the traffic transmitted to some of the hosts might be dropped.
Passive ARP learning enables the ARP cache in the backup router to hold approximately
the same contents as the ARP cache in the master router, thus preventing the problem
of learning ARP entries in a burst. To enable passive ARP learning, include the
statement at the
passive-learning
[edit system arp]
passive-learning;
We recommend setting passive learning on both the backup and master VRRP routers.
Doing so prevents the need to manually intervene when the master router becomes the
backup router. While a router is operating as the master router, the passive learning
configuration has no operational impact. The configuration takes effect only when the
router is operating as a backup router.
For information about configuring gratuitous ARP and the ARP aging timer, see the Junos
OS Administration Library.
hierarchy level:
[edit system arp]
Chapter 14: Configuring VRRP
(10
startup-silent-period
startup-silent-period
147