Per packet vs per flow routing

Discussion in 'Cisco' started by R Siffredi, Mar 22, 2005.

  1. R Siffredi

    R Siffredi Guest

    I have a question regarding OSPF and how it would handle routing between two T1's by default.
    Is it going to per packet load balance between the T1's OR per flow choose which T1 to utilize for a given flow?

    How do I set this to per flow if no the default.

    Tx
     
    R Siffredi, Mar 22, 2005
    #1
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  2. R Siffredi

    thrill5 Guest

    On Cisco, the default is per flow regardless of your routing protocol.

    Scott
     
    thrill5, Mar 23, 2005
    #2
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  3. R Siffredi

    R Siffredi Guest

    But what will happen on per flow if one of the T1's fills up with
    traffic, is there a way it would know to switch to other T1?

    Should I c onsider a ppp multilink?
     
    R Siffredi, Mar 23, 2005
    #3
  4. R Siffredi

    Hansang Bae Guest

    No. No routing protocol exists that takes load into account. Yes,
    EIGRP *can* use it as a metric, but it's zeroed out by default. Why do
    you suppose that is? The ability to detect congested links and react
    to it intelligently is quite challenging from a routing perspective.


    That's one way to solve it if you have CPU to spare.

    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
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    Hansang Bae, Mar 23, 2005
    #4
  5. R Siffredi

    R Siffredi Guest

    Is there another way to solve it?

    Tx


     
    R Siffredi, Mar 23, 2005
    #5
  6. R Siffredi

    thrill5 Guest

    Unless you have a single source/destination pair that needs more than a T1
    of bandwidth than flow based load balancing will be fine. If this won't
    work, than you can turn on per packet load balancing but it will cost you
    CPU cycles. If you have a low end router be careful. The reason load
    balancing defaults to per flow is because it is less CPU intensive and it
    works just fine 99% of the time.

    Scott
     
    thrill5, Mar 24, 2005
    #6
  7. R Siffredi

    R Siffredi Guest

    Unfortunately, it is a 3825 router and I have a voice and video
    requirement. This eliminates per packet load balance. The endpoints
    are vpn devices, so it is all single source/dest pair and I need at
    least 2Mbps of the bandwidth. The only option then is ppp multilink.
    Correct?

    Thanks for your help
     
    R Siffredi, Mar 24, 2005
    #7
  8. :Unless you have a single source/destination pair that needs more than a T1
    :eek:f bandwidth than flow based load balancing will be fine. If this won't
    :work, than you can turn on per packet load balancing but it will cost you
    :CPU cycles. If you have a low end router be careful. The reason load
    :balancing defaults to per flow is because it is less CPU intensive and it
    :works just fine 99% of the time.

    Unless, that is, you are using CeF -- modern CeF has little to no
    extra overhead to go per-packet. But if you are using flow caching
    instead of CeF, then per-packet balancing requires dropping down to
    process switching.
     
    Walter Roberson, Mar 24, 2005
    #8
  9. R Siffredi

    Hansang Bae Guest


    CEF is a smarter switching method common on all new gear. It uses
    source/destination IP among other things to create the flow.
    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not not be able to
    reply to emails sent to my account. Please post a followup instead.
    ********************************************************************
     
    Hansang Bae, Mar 24, 2005
    #9
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