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High Availability
HA 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 routers. Control Processor Modules .
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Redundancy
The redundancy features enable the duplication of data elements and software functionality to
maintain service continuation in case of outages or component failure.
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.
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Redundancy on page 232
Software Redundancy on page 232
Configuration Redundancy on page 233
Component Redundancy on page 233
Service Redundancy on page 234
Accounting Configuration Redundancy on page 234
Nonstop Forwarding on page 235
Nonstop Routing (NSR) on page 235
CPM Switchover on page 236
Synchronization on page 237
Configuration and boot-env Synchronization on page 237
State Database Synchronization on page 237
OSPF default session timeout is approximately 40 seconds. The timeout intervals are
7950 SR OS Basic System Configuration Guide
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