When to Use the RSM
Using an RSM in conjunction with a Catalyst 5000 can be a very effective combination for medium-sized networks with moderate Layer 3 bandwidth requirements. Although it is faster than most router-on-a-stick implementations, its speed is not enough for many larger campus backbone applications. Instead, it is the RSMs integration into the Catalyst 5000 architecture that makes it most appealing. Features such as ease of configuration, an intuitive interface, a wide range of supported capabilities, and troubleshooting capabilities are its strengths.
The RSM can also be extremely useful for organizations deploying switched infrastructures in remote offices. This requirement can be met by utilizing the Versatile Interface Processor (VIP) option for the RSM. This is a separate card that literally bolts on top of the RSM to become a two-slot card in the Catalyst. The RSM and the VIP do not communicate over the Catalyst backplane. Instead, a pair of ribbon cables are used to create miniature CyBuses as are used in a 7500-style router.
The VIP then accepts a wide variety of 7200-style Port Adapters. This can allow wide-area serial and ATM links to be directly connected to the Catalyst chassis. Therefore, the RSM can not only provide inter-VLAN routing, it can also perform WAN routing duties.
Be careful when using the HSSI port adapter (typically used for T3 connections) with the RSM VIP because it can overload the power supplies on some models. Check the current release notes for the latest list of models that are affected by this.
As discussed earlier, the RSM is a software-based routing device that cannot provide enough Layer 3 performance for larger campus networks on its own. However, another appealing benefit to the RSM is that it can be easily upgraded to provide hardware-based forwarding via MLS, the subject of the next section.