Basic System Configuration Guide System Management
Edition: 01 3HE 11010 AAAC TQZZA 205
6.2.1 High Availability Features
As more and more critical commercial applications move onto the IP/MPLS
networks, providing high availability services becomes increasingly important. This
section describes high availability features for the 7705 SAR. Most of these features
only apply to routers with two Control and Switching Modules (CSMs).
• Redundancy
• Nonstop Routing (NSR)
• In-service Upgrade
• CSM Switchover
• Synchronization
6.2.1.1 Redundancy
The following redundancy features enable the duplication of data elements and
software functionality to maintain service continuation in case of outages or
component failure.
• Software Redundancy
• Configuration Redundancy
• Component Redundancy
• Accounting Configuration Redundancy
• Multi-Chassis LAG Redundancy
6.2.1.1.1 Software Redundancy
Software outages are challenging even when baseline hardware redundancy is in
place. There should be a balance to provide high availability routing; otherwise,
router problems typically propagate throughout the service provider network and
externally to other connected networks possibly belonging to other service providers.
This could affect customers on a broad scale. There are several software availability
features that contribute to the percentage of time that a router is available to process
and forward traffic.
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