High Availability
240 Basic System Configuration Guide
High availability is an important feature in service provider routing systems. High availability
is gaining momentum due to the unprecedented growth of IP services and applications in
service provider networks driven by the demand from the enterprise and residential
communities. Downtime can be very costly, and, in addition to lost revenue, customer
information and business-critical communications can be lost. High availability is the
combination of continuous uptime over long periods (Mean Time Between Failures (MTBF))
and the speed at which failover or recovery occurs (Mean Time To Repair (MTTR)).
The popularity of high availability routing is evident at the network or service provider edge
where thousands of connections are hosted and rerouting options around a failed piece of
equipment can often be limiting. Or, a single access link exists to a customer because of
additional costs for redundant links. As service providers converge business-critical services
such as real-time voice (VoIP), video, and VPN applications over their IP networks, high
availability becomes much more stringent compared to the requirements for best-effort data.
Network and service availability become critical aspects when offering advanced IP services
which dictates that IP routers that are used to construct the foundations of these networks be
resilient to component and software outages.
For high availability configuration information, refer to Synchronization and Redundancy.
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. Most of these features only apply to routers with two
Control Processor Modules (CPM), currently the 7750 SR-7, SR-12, SR-c12, and ESS-7
models.
• Redundancy
→ Software Redundancy
→ Configuration Redundancy
→ Component Redundancy
→ Service Redundancy
→ Accounting Configuration Redundancy
• Nonstop Forwarding
• Nonstop Routing (NSR)
• CPM Switchover
• Synchronization
→ Configuration and boot-env Synchronization
→ State Database Synchronization
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