08-05-2011 04:06 AM - edited 03-04-2019 01:11 PM
hi ,
can any body give clear picture about BGP dampenening
what i understand about this chapter - i mentioned below
1) BGP dampening - help to prevent flap network propagate to neighbor
dampening parameters
1) penatly - one time network flap (up or down) - 1000
2) Half life time - penatly will come to half vale - 15
3) supress - penatly value cross above value - ( dampening status)
R3(config-router)#bgp dampening 15 1000 3000 60
<1-45> Half-life time for the penalty
<1-20000> Value to start reusing a route
<1-20000> Value to start suppressing a route
<1-255> Maximum duration to suppress a stable route
But unable understand
1) history in BGP table
2) Maximum duration to suppress a stable route
any site or video explain concept in depth let me know
08-09-2011 09:54 PM
BGP Route Dampening is a way to suppress flapping routes so that they are "suppressed" instead of being advertised. .An unstable network can cause BGP routes to flap, which can cause other BGP routers in the network to constantly reconverge. This wastes valuable CPU cycles and can cause severe problems in the network. Hence , as a best practice, ISPs use route dampening regularly.
Penalty - An incremented numeric value that is assigned to a route each time it flaps. A route is penalized 1000 every time it flaps. A route is considered to have flapped when we receive a WITHDRAW and then an UPDATE for a route. If we drop and regain our adjacency with a BGP peer we do not assign a penalty to the routes learned from that peer.
Max suppress limit - The longest amount of time that a route can be suppressed. The default is 4x the half life time but can range from 1 to 255.
History entry - An entry used to store flap information. For the purposes of monitoring and calculating the level of oscillation of a route, it is important to store oscillation information in the router. When the route stabilizes, the history entry will become useless and will be flushed from the router.
08-10-2011 01:20 AM
Hi Jyothi,
thanks for you reply
i had some doubt while doing the lab
Router
R1 ----- R2 ----- R3
configuartion
R2 - route dampening enabled
bgp dampening 10 1500 3000 40
Half life time - 10 min
Reuse - 1500
supress - 3000
max- supress - 40 min
R1 - network 10.0.0.0/16 - avg 5 times oscillating (up and down) every minute
frist penatly - R2 ( history table)
four pentaly with 2 mins - R2 ( keep route 10.0/16 - suppress to dampening)
and if you observe
after 13 times network (10.0/16) ( Up and down) only - Flap values increment with 1 value
i have confusion why after 13 times ( flap value +1 and 1000+ penatly)
Suppress
if max supress time expired (40 mins) - whether route flushed out from own table and its should not poplulated to neighbors ( i am right )
if any mistake - correct me
08-10-2011 02:39 AM
to answer your 1st question,
Aroute is considered to have flappedwhen we receive a WITHDRAW and then an UPDATE for a route.
If we DROP and REGAIN our adjacency with a BGP peer we do not assign a penalty to routes learned from peer.
2nd Question :
Here I see
Reuse (1500) > Penality (1000)
If penalty is less than the reuse limit , a supressed route i.e up will no longer be supressed.
The default value of Reuse is 750 and can range from 1 to 20000
~Jyoti
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