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Forum Replies

  1. Hi Rob,

    Good question! Fast switching only looks at the IP packet and I believe it considers everything with the same destination IP address as to be in the same
    flow, that's it.

    Some other protocols that use flows (like netflow) check many different fields including source/dest port, source/dest address, TOS byte, etc.


  2. Hi Andrew!,

    Glad to see you around and yea! thanks for confirming my doubt.

    I have a few more doubts that i have no where to turn to and i hope you will enlightened me..

    My coreswitch has ip cef turn on my default.

    q1) I have been reading up abit on cisco about IP CEF and it seems like to enable/disable IP CEF, you have to do in at the ingress interface as the decision (e.g. load balance is done there). -- is it right ?

    Assuming i have "no ip cef" and only wish to turn on ip cef on certain interfaces and ->
    q2) if i want to do to packet loadbalancing, should "ip load-share per packet" command be issue on the ingress interface as well ?

    q3) Reading How to Verify Cisco Express Forwarding -> "http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-120-mainline/47205-cef-whichpath.html"

    Use the show interface x/x stat command and determine the number of packets and bytes that the router forwarded through "Processor" instead of "Route cache." Note that "Route cache" includes both fast-switched and CEF-switched packets.

    router#show interface stats     
    Switching path Pkts In  Chars In Pkts Out Chars Out 
    Processor 95084 26211621 33493 3386174 
    Route cache 24581 1132797 24542 13297583 
    Distributed cache 0 0 0 0 
    Total  119665 27344418 58035 16683757

    Should this command be issue on the ingress or egress interface ?
    if it is to be issue on the INGRESS interface -> What does the "Pkts Outs" under Route cache means then ?

    Really hope to hear from you soon.


  3. andrew says:
    1. The ARP table is stored in RAM, and not in either CAM or TCAM

    2. Here is the Cisco definition of Epoch and how it is used:

    The term "epoch" refers to a period of time. A new epoch for a Cisco Express Forwarding table begins when a table rebuild is initiated. The time after this instant is in an epoch different from the time before, and the different epochs are numbered between 0 and 255. Through the use of epochs, the software can distinguish between old and new forwarding information in the same database structure and can retain the old Cisco Express Forwarding database table while the software builds a new table. This is called epoch tracking and it allows Cisco Express Forwarding forwarding to continue uninterrupted while new Cisco Express Forwarding tables are being constructed, and it makes possible a seamless switchover when the new table becomes active

    When you issue a show ip cef <route>, the dependencies output means how many other routes depend (are resolvable through) the <route> you looked up via the CEF command.

  4. Hello Chandrakant.

    I believe you are correct. Actually, those two commands should be on for each of the R1 and R2 routers like so:

    R2(config)#ip route

    R1(config)#ip route

    I will let Rene know so it can be corrected.

    Thanks very much!


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