Cisco CEF Questions

Discussion in 'Cisco' started by Jeff Mac Pherson, Jan 19, 2004.

  1. I'm learning CEFs and basically setting up a new network with a pair
    of T1s. So far I haven't read much, any decent books on CEF ? I
    check my some of my old cisco books and they have no mention of CEF.

    So far, from all the post I read, just enter "ip cef" and it'll be
    enable.

    How do I know it's actually working ? I try to download a few 20 meg
    file but it doesn't seem like its any faster. If anyone has any faq
    or books recommendation, please let me know.. thanks.
    Jeff Mac Pherson, Jan 19, 2004
    #1
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  2. Jeff Mac Pherson

    chris kane Guest

    "Jeff Mac Pherson" <> wrote in message
    news:...
    > I'm learning CEFs and basically setting up a new network with a pair
    > of T1s. So far I haven't read much, any decent books on CEF ? I
    > check my some of my old cisco books and they have no mention of CEF.
    >
    > So far, from all the post I read, just enter "ip cef" and it'll be
    > enable.
    >
    > How do I know it's actually working ? I try to download a few 20 meg
    > file but it doesn't seem like its any faster. If anyone has any faq
    > or books recommendation, please let me know.. thanks.


    Here's a link to a Cisco White Paper (requires CCO login)

    http://www.cisco.com/warp/customer/cc/pd/iosw/iore/tech/cef_wp.htm

    Here's my current favorite Cisco link. Its a list of all technologies.
    You'll find info on CEF under the 'IP Switching and Tunneling' section

    http://www.cisco.com/pcgi-bin/Support/browse/index.pl?i=Technologies&f=372&v
    iewall=true

    As for books - Building Cisco Multilayer Switched Networks (Cisco
    Press/Karen Webb) does have a section dedicated to CEF. I wouldn't buy this
    book soley for that purpose...but if you need help with MLS then its a
    decent book to have around.

    -chris
    chris kane, Jan 19, 2004
    #2
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  3. Jeff Mac Pherson

    Hansang Bae Guest

    In article <>,
    says...
    > I'm learning CEFs and basically setting up a new network with a pair
    > of T1s. So far I haven't read much, any decent books on CEF ? I
    > check my some of my old cisco books and they have no mention of CEF.
    > So far, from all the post I read, just enter "ip cef" and it'll be
    > enable.


    It's IOS/hardware dependent. Some require other keywords, but for the
    most part, "ip cef" will do it.


    > How do I know it's actually working ? I try to download a few 20 meg
    > file but it doesn't seem like its any faster. If anyone has any faq
    > or books recommendation, please let me know.. thanks.


    CEF will not use both links at once unless you use "per-packet" keyword.
    Even then, you *may* get out of sequenced packets. One of my colleagues
    this this several years ago and have not had any issues. Your mileage
    may vary.

    If you want to know more about cef, read "IOS Architecture" book by Russ
    White et al. Great book.



    --

    hsb

    "Somehow I imagined this experience would be more rewarding" Calvin
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    Hansang Bae, Jan 19, 2004
    #3
  4. On 19 Jan 2004 12:55:50 -0800, (Jeff Mac Pherson)
    wrote:

    >I'm learning CEFs and basically setting up a new network with a pair
    >of T1s. So far I haven't read much, any decent books on CEF ? I
    >check my some of my old cisco books and they have no mention of CEF.
    >
    >So far, from all the post I read, just enter "ip cef" and it'll be
    >enable.
    >
    >How do I know it's actually working ? I try to download a few 20 meg
    >file but it doesn't seem like its any faster. If anyone has any faq
    >or books recommendation, please let me know.. thanks.


    See http://www.cisco.com/warp/public/105/cef_whichpath.html

    -Terry
    Terry Baranski, Jan 20, 2004
    #4
  5. Phillip Remaker, Jan 20, 2004
    #5
  6. Jeff Mac Pherson

    AnyBody43 Guest

    (Jeff Mac Pherson) wrote in message news:<>...
    > I'm learning CEFs and basically setting up a new network with a pair
    > of T1s. So far I haven't read much, any decent books on CEF ? I
    > check my some of my old cisco books and they have no mention of CEF.
    >
    > So far, from all the post I read, just enter "ip cef" and it'll be
    > enable.
    >
    > How do I know it's actually working ? I try to download a few 20 meg
    > file but it doesn't seem like its any faster. If anyone has any faq
    > or books recommendation, please let me know.. thanks.


    Hi,

    "but it doesn't seem like its any faster"
    The key question here would seem to be 'What performance do I
    have now and what performance should I expect when CEF is enabled."

    CEF != Faster


    For example:
    1.
    Many platforms will manage to do per packet load sharing on a
    pair of T1's on process switching.

    2.
    If you have a long link (000's miles) then the protocol that you are
    using may not be able to fill one T1 never mind two.


    If you want higher performance for single sessions you should
    consider Multilink PPP. If you search you should find a recent
    thread discussing this, a search for [anybody43 MLPPP] should
    find it.

    My most memorable example of not being able to fill a line
    involved a T3 (I think, 45Mbps anyway) across the Atlantic.
    It proved to be the case that a Windows Explorer file copy
    (a whole c: Drive) could only drive the link at 30k bps.

    So let's see: 30,000/45,000,000 = 1/1500th max capacity.

    This is an extreme (I hope) example of a high
    bandwidth * delay product link and a protocol
    not well suited to the purpose.

    BTW
    A better way to quickly copy a whole windows C: drive across
    the atlantic might be to zip up the whole drive and then to use
    FTP to copy the file. Even then to actually saturate the link
    the TCP receive window would need to be greater than
    45,000,000 bits/sec * 0.1 secs or 500000 bytes!!!

    I usually test links for capacity using FTP, I add
    sessions until the total bandwidth in use stops increasing.
    There are better tools available but then I would need to
    learn how to drive them and I don't do that sort of thing much.
    AnyBody43, Jan 20, 2004
    #6
  7. Jeff Mac Pherson

    MC Guest

    Now somneone please correct me if I am wrong, been a while since I messed
    with CEF.

    If I recall, I believe which process on the router does the switching, fast,
    CEF, etc is detemined on the ingress interface.

    For example, if incoming packet through an Ethernet interface, out two T1
    lines bulnded as a CEF pair, Then CEF would need to be enabled on the
    Ethernet not the T1 lines ????

    In any case, CEF is desirable on amny router setups to fast process packets
    even if not loadbalancing accrosss ciruits just to mimize affect on CPU for
    some forms of attacks.

    Maybe if I get the chance I will go back and review all my past notes and
    share some insight on how I have set this up in the past.

    MC
    "AnyBody43" <> wrote in message
    news:...
    > (Jeff Mac Pherson) wrote in message

    news:<>...
    > > I'm learning CEFs and basically setting up a new network with a pair
    > > of T1s. So far I haven't read much, any decent books on CEF ? I
    > > check my some of my old cisco books and they have no mention of CEF.
    > >
    > > So far, from all the post I read, just enter "ip cef" and it'll be
    > > enable.
    > >
    > > How do I know it's actually working ? I try to download a few 20 meg
    > > file but it doesn't seem like its any faster. If anyone has any faq
    > > or books recommendation, please let me know.. thanks.

    >
    > Hi,
    >
    > "but it doesn't seem like its any faster"
    > The key question here would seem to be 'What performance do I
    > have now and what performance should I expect when CEF is enabled."
    >
    > CEF != Faster
    >
    >
    > For example:
    > 1.
    > Many platforms will manage to do per packet load sharing on a
    > pair of T1's on process switching.
    >
    > 2.
    > If you have a long link (000's miles) then the protocol that you are
    > using may not be able to fill one T1 never mind two.
    >
    >
    > If you want higher performance for single sessions you should
    > consider Multilink PPP. If you search you should find a recent
    > thread discussing this, a search for [anybody43 MLPPP] should
    > find it.
    >
    > My most memorable example of not being able to fill a line
    > involved a T3 (I think, 45Mbps anyway) across the Atlantic.
    > It proved to be the case that a Windows Explorer file copy
    > (a whole c: Drive) could only drive the link at 30k bps.
    >
    > So let's see: 30,000/45,000,000 = 1/1500th max capacity.
    >
    > This is an extreme (I hope) example of a high
    > bandwidth * delay product link and a protocol
    > not well suited to the purpose.
    >
    > BTW
    > A better way to quickly copy a whole windows C: drive across
    > the atlantic might be to zip up the whole drive and then to use
    > FTP to copy the file. Even then to actually saturate the link
    > the TCP receive window would need to be greater than
    > 45,000,000 bits/sec * 0.1 secs or 500000 bytes!!!
    >
    > I usually test links for capacity using FTP, I add
    > sessions until the total bandwidth in use stops increasing.
    > There are better tools available but then I would need to
    > learn how to drive them and I don't do that sort of thing much.
    MC, Jan 24, 2004
    #7
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