[isp-caching] Re: High CPU with WCCP

[Lincoln Dale]

At 03:33 PM 30/10/2002 -0800, Rick Ernst wrote:

:>what you're most likely seeing is that without WCCP, you have traffic being
:>forwarded locally on each linecard.
:>in cisco parlance, that is called "distributed switching" -- typically
:>"distributed cef".
:>
:>on IOS 12.1E, when you enable WCCP, WCCP isn't in the "distributed" path,
:>but only operates centrally, so all linecards have to forward all the
:>traffic via the central processor (RSP).
:>that will mean that WCCP will work, but a bad side-effect is that the RSP
:>is now really really busy. bad.
:>
:>you should look at running IOS 12.0S (the "S Train")
:>[http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/index.html]
:>12.0S is the train that is meant to be used by service-providers.
:>
:>in 12.0S, WCCP can operate on each linecard on a 75xx -- so you'll end up
:>with WCCP "distributed" across each linecard.
:>CPU on the RSP will be a lot happier.
:>details of the enhancements to WCCP that were added to 12.0S are detailed
:>at
:>http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/prod_release_note09186a0080088244.html#xtocid280

Does this apply even with the ACL only pushing a tiny amount of traffic to WCCP?

yes. basically, it means that each Linecard is only smart enough to know that WCCP is operating centrally and that it has no knowledge of what implications that may have on switching packets -- so it'll forward all traffic to the RSP.

with WCCP operating on each Linecard, it can keep all processing local.


cheers,

lincoln.
PS. adding an ACL for WCCP really doesn't change the amount of CPU spent in WCCP significantly. its still inspecting every packet. things to use are: (1) input-based WCCP, (2) BGP Policy Propogation for WCCP -- if you're only interested in inspecting some traffic, use those tools and you'll probably not even notice any cpu increment on any linecard.




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