Memory Planning for Healthy Network Growth

The most costly and easily prevented problem in networks is running out of router memory. You need to have sufficient memory to run Cisco IOS Software that supports your future business needs. For example, you might want to deploy voice, enhance performance, or integrate security into your network in the future. You need to forecast the DRAM and the flash memory requirements for such additions, as described in How to Choose a Cisco IOS Software Release.

The High Cost of Memory Capacity Problems

One reason for the high cost of increasing memory is the cost of the memory itself. Cisco memory is high quality—and expensive. Cisco selects memory vendors very carefully, screening for and rejecting low-quality memory.

Even if memory was free, increasing the memory capacity of hundreds or thousands of routers distributed over a large network would cost a great deal. The cost of buying extra Cisco memory when you order hardware pales in comparison to the pain of boosting the memory of devices already installed. You have to take them out of commission, open them, snap in new memory, and finally bring the routers back into operation. The larger your network, the greater the impact on your operating expenses and your total cost of ownership (TCO).

How to Avoid the Pain

Cisco's prescription for preventing memory capacity problems is to purchase routers with enough memory to meet feature expectations for the entire life of the product, plus a little more as a safety net.

How Much Memory Is Enough?

There's no standard rule for forecasting memory needs. Figure 1 shows the increase in memory requirements of Cisco IOS 12.3T, 12.4T, and future 12.5T for the Cisco 3845 router. The graph for the same releases on another platform might be quite different. The release, the features running on the release, and the hardware have to be taken into account.

Figure 1 Memory required for a Cisco 3845 Router to support growth of network

Memory requirements grow more dramatically for the edge than for the core. Release Notes and Product Bulletins published with each major hardware and software release describe which features will be supported over the next 18 months and how much memory is required. To determine how much memory you need, read Release Notes and Product Bulletins.

Related Information: Determining How Much Memory Is Installed