BGP dampening question

Half-time = 15 min

Reuse = 750

Suppress = 2000

Max-Suppress-time = 60

When the penalties goes above 2000, the route will be supressed, and assume the route becomes stable after that, the route will decrease to 1000 after 15 minutes, and then after 5 seconds, the route decreases again to 500 which is below the Resue (750) so the route becomes active again.

Is this statement correct?

What happen when the penalties stay above 2000 for more than 60 minutes which passes the Max-Suppress-Time?

Thanks in advance!

Comments


  • The max-suppress-time is the worst the penalty can get.  I don't know what the actual number would be, but say the route flaps and flaps and flaps and ..... and keeps building up its penalty.  Instead of the penalty increasing to infinite, it will stop increasing when it gets to the number defined by max-suppress-time.  I guess the idea is you don't want the penalty to get so bad that even after the flapping stops the route will take forever to become useable again.


  • I'm not sure where the 5 second part came from... 

    It's an exponentially decaying rate.  It's not like you stay at 2000 for 15 minutes and then POOF you are at 1000.  It's a sliding scale.  So BY 15 minutes you'll hit 1000 and continue to decay.  You'll decay at a slower rate though because in the same 15 minutes you only need to lose 500 points this time.  But somewhere in the 7.5 MINUTE range, you'll go below 750 and will be readvertised.

    If you stay above 2000 for longer than 60 minutes, your penalty is merely erased.  The assumption is that if you are still having problems you'll get dampened again.

    HTH,

    Scott







    ----- Original Message -----
    From: "VirtualGuy" <[email protected]>
    Sent: Fri, March 27, 2009 13:03
    Subject: [CCIE R&S] BGP dampening question


    Half-time = 15 min

    Reuse = 750

    Suppress = 2000

    Max-Suppress-time = 60

    When the penalties goes above 2000, the route will be supressed, and assume the route becomes stable after that, the route will decrease to 1000 after 15 minutes, and then after 5 seconds, the route decreases again to 500 which is below the Resue (750) so the route becomes active again.

    Is this statement correct?

    When happen when the penalties stay above 2000 for more than 60 minutes which passes the Max-Suppress-Time?

    Thanks in advance!



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  • " If you stay above 2000 for longer than 60 minutes, your penalty is merely erased.  The assumption is that if you are still having problems you'll get dampened again. "

    hey scott i am little confused by the above statement by erased you mean that it will be all gone in other words it will be set to 0... and once it's all gone the route will be advertised again and if still it's flapping it will start getting the penelaty...

    Thanks

    Peace

  • Yup.  Because, lets say something really bad happened and a link/session flapped like 20 times in a minute.

    From 20,000 to 10,000 to 5,000 to 2,500 to 1,500 to 750 you'd be at 75 minutes there.  If it flapped more than that, it could be longer. 

    The goal isn't to dampen someone into oblivion.  It's to keep stability and sanity in the world's BGP tables!  So penalty would go to 0.  If the link was still flapping, then it would start the process all over again at 2,000.

    HTH,

    Scott







    ----- Original Message -----
    From: "Bored" <[email protected]>
    Sent: Fri, March 27, 2009 17:48
    Subject: Re: [CCIE R&S] BGP dampening question


    " If you stay above 2000 for longer than 60 minutes, your penalty is merely erased.  The assumption is that if you are still having problems you'll get dampened again. "

    hey scott i am little confused by the above statement by erased you mean that it will be all gone in other words it will be set to 0... and once it's all gone the route will be advertised again and if still it's flapping it will start getting the penelaty...

    Thanks

    Peace



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  • Hay Scott

    Plz correct me....if the max supress limte is 60 even the route is still unstable the BGP will not unsuppress it anyway after the max supress time?

  • it will not suppress it, but if its still unstable it will start putting a penality on it and if the penelaity reaches the suppress limit it will start suppressing it again

    Peace

  • It will be unsuppressed, although it may be very brief.  You have to remember that there are other timers involved with BGP.  The overall scan time, the database walker, the update timers...  So it may well be that the route is unsuppressed, and if still THAT unstable, it accumulates further penalties and is re-suppressed before actually being advertised out.

    We're playing a theorhetical game here.  These aren't going to be perfect for every what-if situation.  :)  They are in place to hopefully stop everyone from replicating messages around the world constantly saying "I have a route" then "nope, no route" then "I have a route" then "nope, no route"...  Gets a little monotonous especially when rippling through all of the bgp peers!

    Check out RFC 2439.  That's where route dampening is fully defined.  Specifically look at definitions:

    "maximum hold down time (T-hold)
    This value is the maximum time a route can be suppressed no matter how unstable it has been prior to this period of stability."

    HTH,

    Scott





    ----- Original Message -----
    From: "raoburhan" <[email protected]>
    Sent: Sat, March 28, 2009 9:21
    Subject: Re: [CCIE R&S] BGP dampening question


    Hay Scott

    Plz correct me....if the max supress limte is 60 even the route is still unstable the BGP will not unsuppress it anyway after the max supress time?



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  • Thanks for the explainantion scott.

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