Programmable Internetworking & Communication Operating System Docs ... Click Spaces -> Space Directory to see docs for all releases ...
Page tree
Skip to end of metadata
Go to start of metadata

Route Dampening Command Reference

 

admin@XorPlus# set protocols bgp damping disable [true/false]

Note: This command is to Enable/Disable route dampening.

 

admin@XorPlus# set protocols bgp damping half-life [1-45 minutes]

Note: This command is to set the A configurable numeric value that describes the amount of time that must elapse to reduce the penalty by one-half, the default value is 15 minutes.

 

admin@XorPlus# set protocols bgp damping max-suppress [1-720 minutes]

Note: This command is to set the max-suppress timer, it’s default value is 60 minutes.

 

admin@XorPlus# set protocols bgp damping reuse [1-20000 seconds]

Note: This command is to set A configurable numeric value that is compared with the penalty. If the penalty is less than the reuse limit, a suppressed route that is up will no longer be suppressed, the default value is 750.

 

admin@XorPlus# set protocols bgp damping suppress [1-20000 seconds]

Note: This command is to set a numeric value that is compared with the penalty. If the penalty is greater than the suppress limit, the route is suppressed; the default value is 3000.

 

Another mechanism for controlling route instability is route dampening. A route that appears and disappears intermittently causes BGP UPDATE and WITHDRAWN messages to be repeatedly propagated on the Internet. The tremendous amount of routing traffic generated can use up all the link's bandwidth and drive up CPU utilization of routers.

Dampening categorizes routes as well either behaved or ill behaved. A well-behaved route shows a high degree of stability during an extended period of time. On the other hand, an ill behaved route experiences a high level of instability in a short period of time. Ill-behaved routes should be penalized in a way that is proportional to the route's expected future instability. An unstable route should be suppressed (not advertised) until there is some degree of confidence that the route has become stable. 

A route's recent history is used as a basis for estimating future stability. To track a route history, it is essential to track the number of times the route has flapped over a period of time. Under route dampening, each time a route flaps, it is given a penalty. Whenever the penalty reaches a predefined threshold, the route is suppressed. The route can continue to accrue penalties even after it is suppressed. The more frequently a route oscillates in a short amount of time, the faster the route is suppressed. 

Similar criteria are put in place to un-suppress a route and start readvertising it. An algorithm is implemented to decay (reduce) the penalty value exponentially. 

Penalty 

An incremented numeric value that is assigned to a route each time it flaps.

Half-life

A configurable numeric value that describes the amount of time that must elapse to reduce the penalty by one-half.

Suppress Limit

A numeric value that is compared with the penalty. If the penalty is greater than the suppress limit, the route is suppressed.

Reuse Limit

A configurable numeric value that is compared with the penalty. If the penalty is less than the reuse limit, a suppressed route that is up will no longer be suppressed.

Max-suppress Timer

It is the maximum time the BGP route was suppressed.

 

The following figure illustrates the process of assessing a penalty to a route every time it flaps. The penalty is exponentially decayed according to parameters such as the half-life. The half-life parameter can be changed by the administrator to reflect the oscillation history of a route: A longer half-life might be desirable for a route that has a habit of oscillating frequently. A larger half-life value would cause the penalty to decay more slowly, which translates into a route's being suppressed longer.

                              Figure 4-1 Route Dampening Penalty Assessment

 

Configuration Example 1:

                                                        Figure 4-2


Step 1: Switch A, Switch B Establishing EBGP

Switch A:

admin@XorPlus# set protocols bgp bgp-id 9.9.9.9
admin@XorPlus# set protocols bgp local-as "9"
admin@XorPlus# set protocols bgp peer 3003::1 local-ip "3003::2"
admin@XorPlus# set protocols bgp peer 3003::1 as "6"
admin@XorPlus# set protocols bgp peer 3003::1 ipv6-unicast true

Switch B:

admin@XorPlus# set protocols bgp bgp-id 6.6.6.6
admin@XorPlus# set protocols bgp local-as "6"
admin@XorPlus# set protocols bgp peer 3003::2 local-ip "3003::1"
admin@XorPlus# set protocols bgp peer 3003::2 as "9"
admin@XorPlus# set protocols bgp peer 3003::2 ipv6-unicast true

 

Step 2: Switch A propagate a BGP route entry 9999::/64 to Switch B, then check the BGP route table on Switch B

Switch B BGP route table:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete 
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 9999::/64                     3003::2                   9.9.9.9          9 10 i
admin@XorPlus# run show bgp routes ipv6 deatil
Invalid IPNet
admin@XorPlus# run show bgp routes ipv6 detail
9999::/64
        From peer: 9.9.9.9
        Route: Winner
        Origin: IGP
        AS Path: 9 10
        Nexthop: 3003::2
        Multiple Exit Discriminator: 0
        Local Preference: 100
admin@XorPlus#

 

Step 3: Enable BGP Route Dampening on Switch B

admin@XorPlus#set protocols bgp damping disable false

Note: The default half-life: 15, the default max-suppress: 60, the default reuse: 750, the default suppress: 3000.

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete 
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 9999::/64                     3003::2                   9.9.9.9          9 10 i
admin@XorPlus# run show bgp routes ipv6 detail
9999::/64
        From peer: 9.9.9.9
        Route: Winner
        Origin: IGP
        AS Path: 9 10
        Nexthop: 3003::2
        Multiple Exit Discriminator: 0
        Local Preference: 100
admin@XorPlus#

 

Step 4: Withdraw and update the BGP route entry on Switch A and repeat the operation three times, then check the BGP route table, the BGP route entry should be suppressed after the third times.

The first time:

Switch B BGP route table:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete 
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 9999::/64                     3003::2                   9.9.9.9          9 10 i
admin@XorPlus# run show bgp routes ipv6 detail
9999::/64
        From peer: 9.9.9.9
        Route: Winner
        Origin: IGP
        AS Path: 9 10
        Nexthop: 3003::2
        Multiple Exit Discriminator: 0
        Local Preference: 100
admin@XorPlus#
 

The second time:

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete 
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 9999::/64                     3003::2                   9.9.9.9          9 10 i
admin@XorPlus# run show bgp routes ipv6 detail
9999::/64
        From peer: 9.9.9.9
        Route: Winner
        Origin: IGP
        AS Path: 9 10
        Nexthop: 3003::2
        Multiple Exit Discriminator: 0
        Local Preference: 100
admin@XorPlus#

The third time: 

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete 
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
admin@XorPlus#

Note: We can see that the BGP route was suppressed on Switch B the third time you've withdrawn the BGP route entry, and the BGP route entry will be recover after 60 minutes.

60 minutes later :

admin@XorPlus# run show bgp routes ipv6
Status Codes: * valid route, > best route
Origin Codes: i IGP, e EGP, ? incomplete
   Prefix                        Nexthop                   Peer             AS Path
   ----------------------------  ------------------------  ---------------  ------------
*> 9999::/64                     3003::2                   9.9.9.9          9 10 i
admin@XorPlus# run show bgp routes ipv6 detail
9999::/64
        From peer: 9.9.9.9
        Route: Winner
        Origin: IGP
        AS Path: 9 10
        Nexthop: 3003::2
        Multiple Exit Discriminator: 0
        Local Preference: 100
admin@XorPlus#

 

4.2 BGP fast-external-fallover

BGP fast-external-fallover Commands References:

admin@XorPlus#set protocols bgp fast-external-fallover disable [true/false]

Note: BGP fast-external-fallover is enabled by default. The BGP fast-external-fallover command is used to disable or enable fast-external-fallover for BGP peering sessions with directly connected external peers. The session is immediately reset if link goes down, and only directly connected peering sessions are supported.

If BGP fast-external-fallover is disabled, The BGP routing process will wait until the default hold timer expires to reset the peering session.


Configuration Example 2:

                                                   Figure 4-3

Step 1: SwitchA, SwitchB Establishing EBGP

Switch A:

admin@XorPlus# set protocols bgp bgp-id 9.9.9.9
admin@XorPlus# set protocols bgp local-as "9"
admin@XorPlus# set protocols bgp peer 3003::1 local-ip "3003::2"
admin@XorPlus# set protocols bgp peer 3003::1 as "6"
admin@XorPlus# set protocols bgp peer 3003::1 ipv6-unicast true

Switch B:

admin@XorPlus# set protocols bgp bgp-id 6.6.6.6
admin@XorPlus# set protocols bgp local-as "6"
admin@XorPlus# set protocols bgp peer 3003::2 local-ip "3003::1"
admin@XorPlus# set protocols bgp peer 3003::2 as "9"
admin@XorPlus# set protocols bgp peer 3003::2 ipv6-unicast true

Then check BGP peer status on Switch A, SwitchB:

Switch A:

admin@XorPlus# run show bgp peers detail
Peer 1: local 3003::2/179 remote 3003::1/38709
  Peer ID: 6.6.6.6
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 6
  Updates Received: 0,  Updates Sent: 7
  Messages Received: 10,  Messages Sent: 17
  Time since last received update: n/a
  Number of transitions to ESTABLISHED: 2
  Time since last entering ESTABLISHED state: 230 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds

Switch B:

admin@XorPlus# run show bgp peers detail
Peer 2: local 3003::1/38709 remote 3003::2/179
  Peer ID: 9.9.9.9
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 9
  Updates Received: 7,  Updates Sent: 0
  Messages Received: 18,  Messages Sent: 11
  Time since last received update: 227 seconds
  Number of transitions to ESTABLISHED: 1
  Time since last entering ESTABLISHED state: 255 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds

 

Step 2: Shutdown the link BGP peer connected then check the BGP peer status, the BGP peer will be down immediately as BGP fast-external-fallover is enable by default.

admin@XorPlus# set interface gigabit-ethernet te-1/1/46 disable true
admin@XorPlus# commit
Merging the configuration.
Commit OK.
Save done.
admin@XorPlus# run show bgp peers detail 3003::2
Peer 1: local 3003::1/179 remote 3003::2/179
  Peer ID: none
  Peer State: CONNECT
  Admin State: START
  Negotiated BGP Version: n/a
  Peer AS Number: 9
  Updates Received: 0,  Updates Sent: 0
  Messages Received: 0,  Messages Sent: 0
  Time since last received update: n/a
  Number of transitions to ESTABLISHED: 1
  Time since last in ESTABLISHED state: 11 seconds
  Retry Interval: 120 seconds
  Hold Time: n/a,  Keep Alive Time: n/a
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds
admin@XorPlus#

 

Step 3: Up the link BGP peer connected and disable BGP fast-external-fallover on Switch A

admin@XorPlus# set interface gigabit-ethernet te-1/1/46 disable false
admin@XorPlus# commit
Merging the configuration.
Commit OK.
Save done.
admin@XorPlus# set protocols bgp fast-external-fallover disable true
admin@XorPlus# commit
Merging the configuration.
Commit OK.
Save done.
admin@XorPlus#
admin@XorPlus# run show bgp peers detail 3003::2
Peer 1: local 3003::1/52347 remote 3003::2/179
  Peer ID: 9.9.9.9
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 9
  Updates Received: 1,  Updates Sent: 0
  Messages Received: 3,  Messages Sent: 2
  Time since last received update: 4 seconds
  Number of transitions to ESTABLISHED: 2
  Time since last entering ESTABLISHED state: 4 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds

 

Step 4: Shutdown the link BGP peer connected, then check the BGP peer status, the BGP peer will not shutdown immediately, but it will goe down after 90 seconds

admin@XorPlus# set interface gigabit-ethernet te-1/1/46 disable true
admin@XorPlus# commit
Merging the configuration.
Commit OK.
Save done.
admin@XorPlus# run show bgp peers detail 3003::2
Peer 1: local 3003::1/52347 remote 3003::2/179
  Peer ID: 9.9.9.9
  Peer State: ESTABLISHED
  Admin State: START
  Negotiated BGP Version: 4
  Peer AS Number: 9
  Updates Received: 1,  Updates Sent: 0
  Messages Received: 7,  Messages Sent: 7
  Time since last received update: 139 seconds
  Number of transitions to ESTABLISHED: 2
  Time since last entering ESTABLISHED state: 139 seconds
  Retry Interval: 120 seconds
  Hold Time: 90 seconds,  Keep Alive Time: 30 seconds
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds
admin@XorPlus#

90 seconds later :

admin@XorPlus# run show bgp peers detail 3003::2
Peer 1: local 3003::1/179 remote 3003::2/179
  Peer ID: none
  Peer State: ACTIVE
  Admin State: START
  Negotiated BGP Version: n/a
  Peer AS Number: 9
  Updates Received: 0,  Updates Sent: 0
  Messages Received: 0,  Messages Sent: 0
  Time since last received update: n/a
  Number of transitions to ESTABLISHED: 2
  Time since last in ESTABLISHED state: 34 seconds
  Retry Interval: 120 seconds
  Hold Time: n/a,  Keep Alive Time: n/a
  Configured Hold Time: 90 seconds,  Configured Keep Alive Time: 30 seconds
  Minimum AS Origination Interval: 0 seconds
  Minimum Route Advertisement Interval: 0 seconds
admin@XorPlus#
  • No labels