Installation guide
GRP Redundant Processor Support 1
GRP Redundant Processor Support
Feature Summary
The GRP redundant processor feature allows you to install two gigabit route processors (GRPs) in a
Cisco 12000 series router. One GRP functions as the primary processor. The primary GRP supports
all normal GRP operation. The other GRP functions as the secondary processor. The secondary GRP
monitors the primary and will take over normal GRP operations if it detects a failure in the primary
GRP.
The GRP redundant processor feature is not a hot standby system wherein the secondary GRP
duplicates the state of the primary. The benefit of having the secondary GRP monitor the primary,
rather than duplicate the primary, is that a software failure is unlikely to affect both processors. The
tradeoff is that network services will be disrupted while the secondary GRP takes over and the router
recovers. The recovery happens faster, however, than if the router performed a cold restart.
The primary and secondary GRP can be placed in any available card slot in the router chassis. You
may want to consider physical access and cable locations when choosing where to place the GRPs.
Each GRP must have the resources to run the router on its own, which means all GRP resources are
duplicated. In other words, each GRP has its own Flash device, Ethernet, serial, and console port
connections. The console port connections do not use a “Y” cable. Instead, you connect a separate
terminal console cable and monitor to each GRP.
You can access the secondary GRP resources while it is in standby mode. For example, you can use
the copy EXEC command to transfer an image to the secondary GRP flash device. (Refer to “Device
Access,” later in this publication.) By default, the startup-config on the secondary GRP is always
synchronized to the startup-config on the primary.
There are two common ways to use GRP redundant processor support. You can run identical Cisco
IOS software on both GRPs, which protects against GRP hardware failure. Alternatively, you can
run different Cisco IOS images on each GRP. This method is useful, say, when you want to run a
newer Cisco IOS image on one GRP and revert to an older Cisco IOS image if you encounter
problems.
Benefits
The GRP is no longer a single point of hardware failure. Any permanent hardware failure in the
primary GRP is recovered by the secondary GRP, which increases the level of network service and
reliability demanded by customers.
The GRP redundant processor feature is implemented with no impact on the GSR per-line switching
performance, where packet routing is performed by Cisco express forwarding (CEF) in the line
cards.