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Autonomous Switching
With autonomous switching, when a packet arrives on an interface, it is forwarded to the interface processor.
The interface processor checks the silicon−switching cache; if the destination address is not contained in that
cache, the autonomous cache is checked. The packet is encapsulated for autonomous switching and sent back
to the interface processor. The header is not sent to the route processor with this type of switching.
Note Autonomous switching is available only on AGS+ and Cisco 7000 series routers that have high−speed
controller interface cards.
Silicon Switching
Silicon−switched packets use a silicon−switching cache on the Silicon Switching Engine (SSE) found on the
Silicon Switch Processor (SSP). This is a dedicated switch processor used to offload the switching process
from the route processor. Packets must use the router's backplane to get to and from the SSP.
Note
Silicon switching is used only on the Cisco 7000 series router with an
SSP.
Optimum Switching
Optimum switching is similar to all the other switching methods in many ways. As the first packet for a flow
arrives on an interface, it is compared to the optimum switching cache, appended, and sent to the destination
exit interface. Other packets associated with the same session then follow the same path. Just as with process
switching, all the processing is carried out on the interface processor.
Unlike process switching, optimum switching is faster than both fast switching or NetFlow switching when
the route processor is not using policy networking such as access lists. Optimum switching is used on
higher−end route processors as a replacement for fast switching.
Distributed Switching
Distributed switching is used on the VIP cards, which use a very efficient switching processor. Processing is
done right on the VIP card's processor, which maintains a copy of the router's own route cache. This is
another switching type in which the route processor is never copied with the packet header. All the processing
is off−loaded to the VIP card's processor. The router or internal route processor's efficiency is dramatically
increased with a VIP card added.
NetFlow Switching
NetFlow switching is usually thought of as utilizing the NetFlow Feature Card (NFFC) or NFFC II inside the
Catalyst 5000 or 6000 family of switches. These switches use the NFFCs to let a router or internal route
processor make a routing decision based on the first packet of a flow. The NFFCs then determine the
forwarding interface decision made by the router or internal route processor and send all subsequent packets
in the same data flow to that same interface. This method offloads work that the router used to do on to the
switch's NFFC card.
However, NetFlow switching is not just a switching type; it can be used as an administrative tool to gather
statistics in an ATM−, LAN−, and VLAN−implemented network. This type of switching actually creates
some added processing for the router or an internal route processor by collecting data for use with circuit
accounting and application−utilization information. NetFlow switching packets are processed using either the
fast or optimum switching methods, and all the information obtained by this switching type is stored in the
NetFlow switching cache; this cache includes the destination address, source address, protocol, source port,
destination port, and router's active interfaces. This data can be sent to a network management station for
analysis.
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