RE: Netflow Switching and Cisco routers

From: Andrew Fort (
Date: Wed Oct 11 2000 - 18:52:29 PDT

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    > just like to hear from people that are running netflow
    > switching with for
    > example OC3 's on 7XXX and what you're experiences are? Any recommend
    > configurations in terms of hardware and memory?

    When we switched from "fast" switching to Netflow, we also switched from
    using on-board ip accounting ('sh ip account') to using NDE, so I cant gauge
    how much processor load change was due to switching method and how much was
    due to the processor not performing lookups with speed approx. O(n) for the
    ip accounting entries.

    We run a few 7200s with FDDI (for WAN) interfaces. one of them was
    flatlined at 100Mbit/sec for over 12 hours, and the processor didn't

    This is a 7206-NPE200 (not a VXR), mind you (the VXR/NPE-300 doesnt' support
    the FDDI PAs), with 128Mb RAM.

    interface config includes;

     ip route-cache flow
     ip route-cache cef

    global config includes;

    ip cef

    Importantly, turning CEF on gained us about 10-15% of CPU - "IP input"
    process obviously drops to almost 0% (process switching is no longer
    occuring in the majority of first-packet-generating-a-flow cases), and the
    overall CPU load dropped also. It's made the difference between the routers
    running happily, and the routers dropping packets in flash crowd situations
    (most of our traffic is HTTP, so huge numbers of HTTP/1.0 flows cause lots
    of packets to jump to the process level without CEF, killing the routers

    However, the processor load was getting up to 75% or so when the interface
    was maxed, so although we weren't dropping packets, I wouldn't recommend
    running a full-tilt OC3/STM1 interface on a 7206-NPE200 unless there is
    significant CPU advantages in using PoS or ATM interfaces as opposed to FDDI
    (which I dont imagine there would be, but dont have the PoS or ATM
    experience to say...)


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