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

Filter on prefixes i.e. Sprint - Unfriendly
BGP dampening
Throw more money into routers.

Implementation

Try a mixture of all options.

BGP Route Dampening - Solution

Investigate problem

Most flaps by non CIDR origin systems
Most flapping routes are routes with longer prefixes. i.e. /22 or greater
Short prefix routes do not tend to flap.
Reasons ?

Multi-homing
customer networks
no summarisation/CIDRisation on.

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

Router memory
NOC calls
Complexity

Advantages

Advertise fact to encourage CIDR
Lessens load on BGP router/flaps
More stable routing table

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