From: James R. Yeo (james@net-brigade.com)
Date: Mon Mar 15 2004 - 02:13:28 GMT-3
Here is a cut & paste from Cisco.com
Usage Guidelines
IP Route-Cache
Using the route cache is often called fast switching. The route cache
allows outgoing packets to be load-balanced on a per-destination basis
rather than on a per-packet basis. The ip route-cache command with no
additional keywords enables fast switching.
Entering the ip route-cache command has no effect on a subinterface.
Subinterfaces accept the no form of the command; however, this disables CEF
or dCEF on the physical interface as well as all subinterfaces associated
with the physical interface.
IP Route-Cache Same-Interface
You can enable IP fast switching when the input and output interfaces are
the same interface, using the ip route-cache same-interface command. This
configuration normally is not recommended, although it is useful when you
have partially meshed media, such as Frame Relay or you are running Web
Cache Communication Protocol (WCCP) redirection. You could use this feature
on other interfaces, although it is not recommended because it would
interfere with redirection of packets to the optimal path.
IP Route-Cache Flow
The flow caching option can be used in conjunction with CEF switching to
allow statistics to be gathered with a finer granularity. The statistics
include IP subprotocols, well-known ports, total flows, average number of
packets per flow, and average flow lifetime.
IP Route-Cache Distributed
The distributed option is supported on Cisco routers with line cards and
Versatile Interface Processors (VIPs) that support both CEF and flow
switching.
On Cisco routers with Route Switch Processor (RSP) and VIP controllers, the
VIP hardware can be configured to switch packets received by the VIP with
no per-packet intervention on the part of the RSP. When VIP distributed
switching is enabled, the input VIP interface tries to switch IP packets
instead of forwarding them to the RSP for switching. Distributed switching
helps decrease the demand on the RSP.
If the ip route-cache distributed, ip cef distributed, and ip route-cache
flow commands are configured, the VIP will perform distributed CEF
switching and collect a finer granularity of flow statistics.
IP Route-Cache CEF
In some instances, you might want to disable CEF or dCEF on a particular
interface because that interface is configured with a feature that CEF or
dCEF does not support. Because all interfaces that support CEF or dCEF are
enabled by default when you enable CEF operation globally, you must use the
no form of the ip route-cache cef command in the interface configuration
mode to turn CEF operation off a particular interface. To reenable CEF or
dCEF operation, use the ip route-cache cef command.
Disabling CEF or dCEF on an interface disables CEF switching for packets
forwarded to the interface, but has no affect on packets forwarded out of
the interface.
Additionally when you disable CEF or dCEF, Cisco IOS software switches
packets using the next-fastest switching path. In the case of dCEF, the
next-fastest switching path is CEF on the RSP.
Thanks
James
On Fri, 12 Mar 2004 16:28:25 -0500, "Matt Mullen"
<MMullen@nettechgroup.com> wrote :
> Is there any reason to disable fast switching (using 'no ip route-cache)
> on interfaces that have a crypto map applied? The solutions in "CCIE
> Security Practice Labs" say to do this but there is no explanation as to
> why.
>
>
>
> Thanks,
> Matt
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