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JunosE 11.3.x Service Availability Configuration Guide
Unified ISSU
VRRP
Interchassis Redundancy
6
of packets when the fabric is switched from the formerly active line module to the newly
active line module). When resynchronization is completed, the router resumes normal
operations, including updates of any routing tables that result from changes that occurred
during the warm restart.
A conventional software upgrade—one that does not use the unified in-service software
upgrade (ISSU) process—causes a router-wide outage for all users. Only static
configurations (stored on the flash card) are maintained across the upgrade; all dynamic
configurations are lost. A conventional upgrade can take 30-40 minutes to complete,
with additional time required to bring all users back online.
Unified ISSU enables you to upgrade the router to a higher-numbered software release
without disconnecting user sessions or disrupting forwarding through the chassis.
When an application supports unified ISSU, you can configure the application on the
router and proceed with the unified in-service software upgrade with no adverse effect
on the upgrade.
When you perform a unified ISSU on a router that has one or more modules that do not
support unified ISSU, these modules are upgraded by means of the legacy, conventional
upgrade process. The unsupported modules undergo a cold reboot at the beginning of
the unified ISSU process, and are held down until the ISSU process is completed.
Virtual Router Redundancy Protocol (VRRP) prevents loss of network connectivity to
end hosts when the static default IP gateway fails. By implementing VRRP, you can
designate a number of routers as backup routers in the event that the default master
router fails. In case of a failure, VRRP dynamically shifts the packet-forwarding
responsibility to a backup router. VRRP creates a redundancy scheme that enables hosts
to keep a single IP address for the default gateway but maps the IP address to a
well-known virtual MAC address. You can take advantage of the redundancy provided
by VRRP without performing any special configuration on the end host systems.
Routers running VRRP dynamically elect master and backup routers. You can also force
assignment of master and backup routers using priorities in the range 1–255, with 255
being the highest priority.
VRRP supports virtual local area networks (VLANs), stacked VLANs (S-VLANs), and
creation of interchassis redundancy (ICR) partitions.
ICR enables you to minimize subscriber downtime when the router or access interface
on the edge router fails. ICR accomplishes this by re-creating subscriber sessions on the
backup router that were originally terminated on the failed router. It also enables you to
track the failure of uplink interfaces. In this way, ICR enables you to completely recover
from router failure. ICR uses Virtual Router Redundancy Protocol (VRRP) to detect
failures. ICR also enables you to track the failure of uplink interfaces. ICR currently supports
only PPPoE subscribers.
Copyright © 2010, Juniper Networks, Inc.
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