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The steps of packet forwarding inside a router are a processing path, known as Switching Path. There are three kinds of Switching Paths in Cisco routers: Process Switching (PS), Fast Switching (FS) and Cisco Express Forwarding (CEF). Switching Paths affect the packet forwarding performance of routers; therefore, this research is to analyze the effects of Switching Paths on the router performance, indicated by CPU Load. Among Switching Paths, the performance of PS is much lower than other two, so the analysis is focused on the difference between FS and CEF. FS stores into Route Cache the routing information of a packet and the physical address of the next hop the packet forwarded to, and thus with retrieving the information from the cache it can shorten the forwarding delays of the other packets to the same destination network as the packet. Since the physical addresses of next hops are mostly got from ARP Cache, the content of Route Cache will be rebuilt once Route Cache and ARP Cache are not synchronized on physical addresses. The performance of FS is dropped to the same of PS at this moment. CEF stores routing information and the physical addresses of next hops in CEF Table and Adjacency Table, respectively. This helps to avoid performance dropping to the same of PS on the synchronization problem of the physical address information. Cisco declares the performance of CEF is better than that of FS, but has not explained in any open technical literature which factors cause their difference. The result of this research tells Aging Time of ARP Cache is the main factor causing the difference. The contributions are of giving a number of experimental data and analysis methods to explain the different effects on performance of Switching Paths in details. This provides the performance factors as the reference on network planning, and thus helps to handle the performance of routers.
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