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Thread: BGP Question

  1. #1
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    BGP Question

    Is it possible to balance the amount of traffic that goes to different providers?

    The goal would be to have provider A, B and C

    Would like to have a 1gb commit with A, a 100mb commit with B, and a very low commit with C. The idea being to balance out our utilization between A and B, but only use C in case of an emergency.
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  2. #2
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    Do you care to balance only outbound traffic?
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  3. #3
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    that is a good question. Would love to know what the options are and the difficulty for each would be?

    What are your thoughts?
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  4. #4
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    that should be possible through putting the proper costs on each different providers uplink.

    http://www.cisco.com/en/US/tech/tk36...800945bf.shtml
    Last edited by mazedk; 06-07-2011 at 04:46 PM. Reason: link

  5. #5
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    outbound is your only option really isnt it ? - since you'll be telling the sources which way to go to your dest otherwise..

  6. #6
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    Not easy, first remember that commits and charges are based on the 95% of the larger incoming or outgoing sample. Most hosting providers outgoing traffic is higher (serving web pages etc) most normal companies incoming is larger (downloading files etc.)

    With BGP there is no magic to load balance your traffic over multiple links the path chosen is normally the one that traverses the fewer providers. You do have more control over your outgoing traffic than incoming traffic. Normally you control your outgoing traffic by setting a LOCAL_PREFERENCE so provider A is preferred over B for certain internet destinations (nets). For incoming traffic you normally prepend your AS number several times when sending your networks to the provider you would not want to use. Doing either of these could penalize your traffic as it may now take a slower route to the destination.

    One solution (if your traffic is mainly outgoing) is to use a route optimization platform like Internaps FCP this measures latency on the outgoing paths and forces traffic down the fastest path. It can also be configured to use provider A over B if both routes are about the same performance.

    All in all BGP load balancing can get very complex, often it is simpler, cheaper and better to simply get a redundant feed from a single provider that has a good routing mix. (that $40K for an FCP box + 40K for a good BGP capable router could buy many years of 100Meg-1G bandwidth!!!).

    Dave.

  7. #7
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    Quote Originally Posted by mazedk View Post
    that should be possible through putting the proper costs on each different providers uplink.

    http://www.cisco.com/en/US/tech/tk36...800945bf.shtml

    not exactly, this is just giving weight to preferences and letting bgp do its nature.

    Short answer yes you can do this but you can't tell it to "limit" x traffic to a single network and fail the rest over to another link.


    Long answer involves giving higher preferences to specific routes over specific neighbors and balancing the traffic.

    very short answer? get a FCP and let it do its thing with limiting traffic per peer.

  8. #8
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    will an FCP box work with a 6509/sup720-3bxl?
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  10. #10
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    Quote Originally Posted by mazedk View Post
    that should be possible through putting the proper costs on each different providers uplink.

    http://www.cisco.com/en/US/tech/tk36...800945bf.shtml
    Umm, this is fairly crude, at a quick glance it looks like it take the first 1/2 of the address space (0.... -> 127....) and shoves it down provider A and the other half down provider B.

    It is probably better to choose some of the bigger super nets from each prover (for example prover A and its customers) go to A (provider B and its customers) go to B. The others go to the path with the least providers.

  11. #11
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    does using an FCP box require that you use their providers, or does this work with your existing providers?
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  12. #12
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    You can use your current providers. You do not need to be an Inap customer to use the box. They sell it stand alone.

  13. #13
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    Quote Originally Posted by enteracloud View Post
    does using an FCP box require that you use their providers, or does this work with your existing providers?
    No you can use it with any providers. In fact it makes no sense to use it with Internap bandwidth as their network already uses a souped up version to manage its blend of providers to give the best performance.

  14. #14
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    I'm certainly no expert in traffic engineering but in my research I've come across a widely presented paper that covers the topic:

    http://www.nanog.org/meetings/nanog3...ions/smith.pdf

    Look at the section called: Two links to different ISPs

    Announce /19 aggregate on each link
    • Split /19 and announce as two /20s, one on each link basic inbound loadsharing
    • When one link fails, the announcement of the /19 aggregate via the other ISP ensures continued connectivity

    • Loadsharing in this case is very basic
    • But shows the first steps in designing a
    load sharing solution
    Start with a simple concept
    And build on it…!

    • Vary the subprefix size and AS PATH length
    until “perfect” loadsharing achieved
    • Still require redundancy!


    • This example is more commonplace
    • Shows how ISPs and end-sites subdivide
    address space frugally, as well as use the
    AS-PATH prepend concept to optimise the
    load sharing between different ISPs
    • Notice that the /19 aggregate block is
    ALWAYS announce

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