6.1 VLAN Issues
6.1.8 Internal route processors (RSM)
In the Figure, traffic flows to the router from the source VLAN, where it is routed to the destination VLAN. This creates an out-and-back flow to the router. Technically, the switch internal route switch module (RSM) uses a very similar flow, but one important difference is the traffic uses the switch backplane (the high-speed switching path used inside the switch chassis). This difference provides two key benefits:
  • Speed
  • Integration

Because the RSM connects directly to the backplane of the switch, it allows the router to be much more tightly integrated with the switching process. Not only can this ease configuration tasks, but it can provide intelligent communication between the Layer 2 and Layer 3 portions of the network. Also, because it provides a faster link than a single Fast Ethernet ISL interface, performance is improved. In general, the RSM provides 125,000-175,000 packets per second (pps) for IP and approximately 100,000 pps for other protocols. If necessary, more than one RSM can be used in a single switch chassis for additional throughput.