Hi,
At 10:52 AM 6/12/2000 +0900, Kazu Kimura wrote:
>Hello all,
>
>Reviewing Cisco's document in the web page concerning WCCP, I found it
>is a very convenient tool to save the bandwidth to upstream.
>
>But when we consider the introduction, there is a concern to the influence
>to CPU utilization except the cost.
characterizing the impact on cpu utilization when enabling WCCP isn't an
easy thing to do.
for one thing, deploying caching may result in "less packets to the
internet" (assuming the cache is _working_ :-) ), but for another it may
mean more packets _thru_ the router depending on where the caches are
placed relative to the router and where the http requests are coming from
(the web-browser).
WCCP itself is implemented in most switching-paths used on cisco
routers. it exists in dCEF on 75xx, CEF on other platforms on most IOS
12.xx releases and is also implemented in fast- and process-switching paths.
it will actually operate at whatever switching-level packets are already
being "switched at" - and won't cause the switching level to drop to a
lower level on its own.
bearing these things in mind, here's a few general statements:
- use input-based WCCP over output-based WCCP where you can.
if you think thru the logic of "how a router switches a packet", it quickly
becomes apparent that this will mean that the router only has to switch
intercepted packets once (as opposed to twice on output-based WCCP)
- place caches into the network whereby they can "route" back to the
web-browser
NOT thru the router performing interception.
- since a single WCCP service-group can operate on many devices at the
same time, it is better to perform the "intercept/redirect" function
across a bunch
of (say) access-routers than to deploy it on a pair of core routers.
ie. distribute the functionality across multiple devices.
- for ultimate scalability, think about using switching platforms which
support
WCCP and perform packet-switching in hardware.
right now, this means Catalyst 6x00.
with the Catalyst 6500 + PFC2 + MSFC2, there is nothing stopping you from
true wire-rate operation.
cheers,
lincoln.
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