My Presentation at RIPE on BGP route dampening


BGP Route Dampening

Tony Barber

UUNET PIPEX International

Sep 1996


BGP Route Dampening -WHY

  • UUNET PIPEX (AS1849)
  • Memory problems - Route table growth
  • Large instabilities from peers causing problems
  • Now fixed - stop happening again ?
  • CIDR !
    BGP Route Dampening - Options

  • Options
  • Implementation
    BGP Route Dampening - Solution

  • Investigate problem
  • Implement trial solution
    BGP Route Dampening

  • Penalise > /24 routes heavily
  • Penalise >= /22 routes less heavily
  • Penalise all other routes with CISCO standard dampening parameters
  • set dampening
  • set dampening 15 750 2000 30 (def)
  • 1000 penalty for each flap
  • Penalty decays at granularity of 5 seconds
  • Dampening info kept until penalty becomes < half of reuse limit.
    BGP Route Dampening

    - Penalties (Re-use in)
  • /24 and greater =~ 2h 40 minutes
  • /22 and /23 =~ 60 minutes
  • all others =~ 30 minutes (default)
  • Depending on further flaps(Tighten curve)
  • Filter all prefixes > /24
    BGP Route Dampening

  • Disadvantages
  • Advantages
    BGP Route Dampening - Issues

  • Uniform across your Network
  • Inform Helpdesk/NOC
  • Inform Peers
  • Dont dampen default if use it.
  • Specific Problems handled by route map.
  • Possibly handle different peers separately
    BGP Route Dampening - Issues

  • European/Global co-ordination.
  • Best to have all NOCS/Networks in step IMHO.
  • RFC Best Practices/Draft ?
  • Can routing-wg agree on some parameters?
    BGP Route Dampening - samples

    Cisco Samples
    bgp damp route-map expo-flap-dampen
    ! don't dampen default route if receive it
    ! This would not really be a good thing :-)
    ! access-list 4 is the default route only
    route-map expo-flap-dampen permit 5
    match ip address 4
    
    ! Savage dampening of all networks which have a mask of
    ! /24 and above. These are supressed into  a datastructure
    ! with a half life of 45 minutes, only re-use when reaches 250
    ! Max outage of 255 minutes.
    route-map expo-flap-dampen permit 10
    match ip address 181
    set dampening 45 250 2000 255
    
    ! dampen /23 /22
    ! half life is now 25 minutes and reuse at 650
    route-map expo-flap-dampen permit 20
    match ip address 182
    set dampening 25 650 2000 60
    
    ! default dampening on all less than /18 defaults to this
    ! These are the defaults set by the standard
    ! bgp dampening command
    route-map expo-flap-dampen permit 40
    set dampening 15 750 2000 30
    
    ! default dampening on all less than /18 defaults to this
    ! These are the defaults set by the standard
    ! bgp dampening command
    route-map expo-flap-dampen permit 40
    set dampening 15 750 2000 30
    
    Thanks to S Doran and Ravi Chandra for their assistance.

    Mail your abuse to - tony.barber@pipex.net