High Availability
Page 214 7750 SR OS Basic System Configuration Guide
• Nonstop Routing (NSR) on page 217
• CPM Switchover on page 218
• Synchronization on page 219
→ Configuration and boot-env Synchronization on page 219
→ State Database Synchronization on page 219
Redundancy
The redundancy features enable the duplication of data elements and software functionality to
maintain service continuation in case of outages or component failure.
Refer to the 7750 SR-Series OS Integrated Services Adapter Guide for information about
redundancy for the Integrated Service Adapter (ISA).
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 not only throughout the service provider network, but also externally to other connected
networks possibly belonging to other service providers. This could affect customers on a broad
scale. Presently, there are several software availability features that contribute to the percentage of
time that a router is available to process and forward traffic.
To fully appreciate high availability you should realize that all routing protocols specify minimum
time intervals in which the peer device must receive an acknowledgement before it disconnects the
session.
• OSPF default session timeout is approximately 40 seconds. The timeout intervals are
configurable.
• BGP default session timeout is approximately 120 seconds. The timeout intervals are
configurable.
Therefore, router software has to recover faster than the specified time interval to maintain up
time.
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