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Configuring High System Availability
This section describes high system availability (HSA), a feature that enables a router to continue
processing and forwarding packets after a planned or unplanned outage.
It includes the following topics:
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HSA is the system default when two RSP8s, or an RSP8 and an RSP16 (one designated as the "active"
and the other as the "standby") are installed in a router and the active RSP8 fails. The standby RSP8
takes over in this situation, known as a "cold standby." The router restarts without manual intervention
(for example, without inserting a new RSP) by rebooting with the standby RSP. The standby has its own
image and configuration file and acts as a single processor.
Caution
To ensure proper functioning of the standby RSP8 in the event of an active RSP8 failure, the standby
RSP8 should have the same boot image, the same ROM monitor, and the same DRAM configuration
as the active RSP8.
An RSP8 can interoperate with another RSP8, or with an RSP16. It cannot interoperate with an RSP1,
Note
an RSP2, or an RSP4/4+. In the following text, you can substitute references to two RSP8s with an
RSP8 and an RSP16.
When two new RSP8s (or an RSP8 and an RSP16) are installed at the same time, the RSP that occupies
the first even RSP slot on the router is the active (normally the RSP16 if the RSP8 is used in conjunction
with the RSP16), and the RSP that occupies the odd RSP slot is the standby. If a crash has occurred, the
RSP in the odd slot becomes the active and the RSP in the even slot becomes the standby.
HSA is supported on the following routers: Cisco 7507, Cisco 7507-MX, Cisco 7513, and
Cisco 7513-MX. HSA is not supported on the Cisco 7505 or the Cisco 7576 routers.
The cold standby procedure, from initial failure to first packet transmission, currently takes
approximately eight to ten minutes.
For more complete HSA configuration information, refer to the Cisco IOS Configuration Fundamentals
Configuration Guide and the Cisco IOS Configuration Fundamentals Command Reference publications,
which are available online, on the Cisco Documentation CD-ROM, or as printed copies.
HSA Active and Standby Operation
During HSA operation, the active RSP8 card functions as if it were a single processor, controlling all
functions of the router. The standby RSP8 card does nothing but actively monitor the active RSP8 for
failure.
When the standby RSP8 detects a nonfunctional active RSP8, the standby resets itself and takes part in
active-standby arbitration. Active-standby arbitration is a ROM monitor process that determines which
RSP8 card is the active and which is the standby upon startup (or reboot).
OL-4920-02
HSA Active and Standby Operation, page 25
HSA Implementation Methods, page 26
HSA System Requirements, page 27
HSA Configuration Task List, page 27
Monitoring and Maintaining HSA Operation, page 40
Route Switch Processor (RSP8) Installation and Configuration Guide
Configuring High System Availability
25
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