Both the Route Processor and Linecards have a block of memory that is known as "Processor Memory". This block is used as the primary memory location for the operation of Cisco IOS® Software. The complete list of data structures and processes that use this memory is nearly impossible to detail, some of the major consumers of this memory on the Route Processor are as follows.
The 12000 Series Linecards store a subset of the information from the RP and may have other structures that are required only on the Linecards. Here is a brief list of the major consumers of Processor Memory on the Linecards. (Note: not all of these processes/features run on all linecards)
Sufficient Processor Memory is critical to the operation of Cisco IOS Software. Insufficient memory may result in poor or incomplete routing convergence, incorrect packet forwarding, general software instability, and errors in statistics/accounting. For these reasons, we recommend the following memory selections for networks of the given sizes. For MPLS-VPN environments, VPNv4 routes should also be counted against these recommendations in combination with the IPv4 routes in the default routing table.
For networks with 100,000 routes or fewer, Cisco recommends at least 256 MB of RP memory and at least 128 MB of LC memory. For networks with more than 100,000 routes but less than 200,000 routes, Cisco recommends at least 512 MB of RP memory and at least 256 MB of LC memory. For networks with more than 200,000 routes, Cisco recommends using the Performance Route Processor with at least 1 GB of memory and configuring all linecards with the maximum amount of route memory available.
Using the Performance Route Processor should be considered for all networks, as the increased processing power and wider data path to and from the linecards offers significant improvement to routing convergence times.
In addition to Processor Memory options, Cisco provides options for flash-card (or flash-disk) storage on the Route Processor. Today, PCMCIA flash cards/disks are available for ordering on the RP are: 16 MB, 20 MB, 48 MB, 128 MB. PRP flash memory options are 64 MB (default), 128 MB, and 1 GB. With the increasing size of IOS images, it is recommended to use at least a 48 MB flash disk in the Routing Processor. This flash space will allow for multiple IOS images and/or large configurations to be stored locally on the Route Processor.
These recommendations are based on analysis of existing networks as well as significant laboratory testing. It is possible that networks with larger numbers of routes than those recommended here will run without memory problems. However, these recommendations are set out as conservative guidelines, and consider a number of factors such as the growth of the IOS images, addition of future data structures to support new features, as well as providing a block of free memory to guard against transient increases in the global routing table. The amount of used memory, free memory, and the low-water mark for free processor memory may be seen by executing the show memory summary command on the Route Processor and on all Linecards.