When there are several paths available in the routing table, the router will generally alternate between the different possible paths. When you use process switching, the router will alternate packets among the different paths. With Fast Switching, however, it will alternate flows rather than individual packets. For TCP connections, this means that each separate connection will find one of the available paths and use this path exclusively. For UDP and ICMP, however, every packet is a separate flow, so successive packets will likely take different paths.
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