Link Aggregation; Nonstop Active Routing; Nonstop Software Upgrade - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Link Aggregation

Nonstop Active Routing

Nonstop Software Upgrade

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communications. When you configure graceful Routing Engine switchover, the backup
Routing Engine automatically synchronizes with the master Routing Engine to preserve
kernel state information and forwarding state. Any updates to the master Routing Engine
are replicated to the backup Routing Engine as soon as they occur. If the kernel on the
master Routing Engine stops operating, the master Routing Engine experiences a hardware
failure, or 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 the boot 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 to
that of the new master Routing Engine. The interruption to traffic is minimal.
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. In a Virtual
Chassis, LAGs can be used to load-balance network traffic between member switches.
The number of Ethernet interfaces you can include in a LAG and the number of LAGs you
can configure on a switch depend on the switch model.
Nonstop active routing (NSR) provides high availability in a switch with redundant Routing
Engines by enabling transparent switchover of the Routing Engines without requiring
restart of supported routing protocols. Both Routing Engines are fully active in processing
protocol sessions, and so each can take over for the other. The switchover is transparent
to neighbor routing devices, which do not detect that a change has occurred.
To use nonstop active routing, you must also configure graceful Routing Engine switchover.
Nonstop software upgrade (NSSU) is available on EX8200 switches with redundant
Routing Engines. NSSU takes advantage of graceful Routing Engine switchover and
nonstop active routing to enable upgrading the Junos OS version running on a switch
with no disruption to the control plane. In addition, NSSU upgrades line cards one at time,
permitting traffic to continue to flow through the line cards that are not being upgraded.
By configuring LAGs such that the member links reside on different line cards, you can
achieve minimal traffic disruption when performing an NSSU.
For more information on high availability features, see the Junos OS High Availability
Configuration Guide.
EX4200 Virtual Chassis Overview on page 891
EX8200 Virtual Chassis Overview on page 1071
Chapter 1: Software Overview
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