Juniper JUNOS OS 10.3 - SOFTWARE Manual page 118

Complete Software Guide for Junos
Virtual Chassis Software Upgrade and Failover Features
Link Aggregation
Related
Documentation
22
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OS for EX Series Ethernet Switches, Release 10.3
the administrator initiates a manual switchover, mastership switches to the backup
Routing Engine.
When the backup Routing Engine assumes mastership in a redundant failover
configuration (that is, when graceful Routing Engine switchover is not enabled), the
Packet Forwarding Engines initialize their state to boot up state before they connect to
the new master Routing Engine. In contrast, in a graceful switchover configuration, the
Packet Forwarding Engines do not reinitialize their state, but resynchronize their state
with the new master Routing Engine. The interruption to the traffic is minimal.
GRES on EX4200 switches supports software features in Junos OS Release 9.2 or later
for EX Series switches.
EX4200 switches provide these features for increased resiliency in Virtual Chassis
configurations:
Virtual Chassis atomic software upgrade—When you upgrade software in a Virtual
Chassis configuration, the upgrade will either succeed or fail on all member switches,
preventing the situation in which only some of the Virtual Chassis member switches
are upgraded.
Virtual Chassis fast failover—A hardware-assisted failover mechanism that
automatically reroutes traffic and reduces traffic loss in the event of a link failure.
Virtual Chassis split and merge—If there is a disruption to the Virtual Chassis
configuration due to member switches failing or being removed from the configuration,
the Virtual Chassis configuration splits into two separate Virtual Chassis.
You can combine multiple physical Ethernet ports to form a logical point-to-point link,
known as a link aggregation group (LAG) or bundle. A LAG provides more bandwidth than
a single Ethernet link can provide. Additionally, link aggregation provides network
redundancy by load-balancing traffic across all available links. If one of the links should
fail, the system automatically load-balances traffic across all remaining links.
You can select up to eight Ethernet interfaces and include them within a LAG. In an
EX4200 Virtual Chassis configuration, the interfaces that form a LAG can be on different
members of the Virtual Chassis. See "Understanding Virtual Chassis Configurations and
Link Aggregation" on page 932.
For more information on high availability features, see the Junos OS High Availability
Configuration Guide at
http://www.juniper.net/techpubs/software/junos/index.html
Virtual Chassis Overview on page 921
Understanding Virtual Chassis Components on page 924
Understanding Virtual Chassis Configurations and Link Aggregation on page 932
Understanding VRRP on EX Series Switches on page 1671
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