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Cisco 12000 Series Internet Router Configuration Guide for Cisco IOS Release 12.0S
Chapter 2 Basic Configuration of the Cisco 12000 Series Internet Router
Route Processing
Redundant Route Processor Support
As of Cisco IOS Release 12.0(5)S, the Cisco 12000 Series Internet Router supports the installation of
two route processors (RPs). One RP functions as the primary or active processor. The primary RP
supports all normal RP operation. The other RP functions as the secondary or standby processor. The
secondary RP monitors the primary and will take over normal RP operations if it detects a failure in the
primary RP.
Note The redundant RP features are only supported when using two GRPs or two PRPs. There is no support
for redundancy when a GRP is used together with a PRP.
Refer to the following document for further information:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios112/ios112p/gsr/gsr_rp.htm
Route Processor Redundancy Plus (RPR+)
An enhancement to RP redundancy called Route Processor Redundancy Plus (RPR+) was introduced in
Cisco IOS Releases 12.0(17ST) and 12.0(22)S. With RPR+, the standby RP is fully initialized and
configured. This feature allows RPR+ to dramatically shorten the switchover time if the active RP fails
or if a manual switchover is performed. Because both the startup configuration and the running
configuration are continually synchronized from the active to the standby RP, line cards are not reset
during a switchover. The interfaces remain up during this transfer, so neighboring routers do not detect
a link flap (that is, the link does not go down and back up).
Note RPR+ features are only supported when using two GRPs or two PRPs. There is no support for
redundancy when a GRP is used together with a PRP.
The default redundancy mode for Cisco 12000 Series Internet Routers is standard RPR. For information
on configuring RPR+, refer to the following document:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120st/120st17/
rpr_plus.htm
RPR+ is not supported on all Cisco 12000 Series Internet Router line cards. Refer to the Release Notes
for Cisco IOS Release 12.0S for the list of supported line cards.
Cisco Nonstop Forwarding
Cisco Nonstop Forwarding (NSF) is a complementary feature to the Stateful Switchover (SSO) feature
in Cisco IOS software. NSF always runs together with SSO and works with SSO to minimize the amount
of time a network is unavailable to its users following a switchover. The main objective of NSF is to
continue forwarding IP packets following a Route Processor (RP) switchover.
Usually, when a networking device restarts, all routing peers of that device detect that the device went
down and then came back up. This transition results in what is called a routing flap, which could spread
across multiple routing domains. Routing flaps caused by routing restarts create routing instabilities,
which are detrimental to the overall network performance. NSF helps to suppress routing flaps in
SSO-enabled devices, thus reducing network instability.
