Distributed Cef Dcef

One of the main advantages of CEF is that it can be used in a distributed manner. Some Cisco routers use a central CPU without any form of decentralized or distributed intelligence. An example of such a router is the 7200 series router. CEF in this platform can only use the central CPU and as such can forward traffic by the CPU or in interrupt mode. Other hardware—such as the 7500 or GSR 12000 series router—has distributed intelligence and CPUs. Therefore, the router can distribute the burden of forwarding traffic through CEF by using the distributed CPUs to forward traffic without interrupting the central CPU. To achieve the distributed forwarding, both the CEF and adjacency table have to be distributed to these distributed CPUs. For the 7500 series router, the distributed intelligence is present on a Versatile Interface Processor (VIP), and for the GSR 12000 series router, the distributed intelligence is present on the line cards. Figure 6-4 shows a diagram depicting the main CPU of a router with the distributed intelligence on VIPs/line cards. They are all interconnected by means of a bus or switching fabric architecture, which can distribute the CEF and adjacency table.

CEF Switching Packets in Hardware 155

Figure 6-4 Distributed Architectures

Route/Switch Processor (RSP)/Performance Route Processor (PRP)

Route/Switch Processor (RSP)/Performance Route Processor (PRP)

Bus/Switching Fabric

Bus/Switching Fabric

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