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Configuring Damping Parameters (Optional)

Flap damping reduces the number of update messages by marking routes as ineligible for selection as the active or preferable route. Marking routes in this way leads to some delay, or suppression, in the propagation of route information, but the result is increased network stability. You typically apply flap damping to external BGP (EBGP) routes (routes in different ASs). You can also apply flap damping within a confederation, between confederation member ASs. Because routing consistency within an AS is important, do not apply flap damping to internal BGP (IBGP) routes. (If you do, it is ignored.)

You can specify one or more of the damping parameters described in Table 83. If you do not specify a damping parameter, the default value of the parameter is used.

Table 83: Damping Parameters

Damping Parameter

Description

Default Value

Possible Values

half-life minutes

Decay half-life—Number of minutes after which an arbitrary value is halved if a route stays stable.

15 (minutes)

1 through 4

max-suppress minutes

Maximum hold-down time for a route, in minutes.

60 (minutes)

1 through 720

reuse

Reuse threshold—Arbitrary value below which a suppressed route can be used again.

750

1 through 20000

suppress

Cutoff (suppression) threshold—Arbitrary value above which a route can no longer be used or included in advertisements.

3000

1 through 20000

To change the default BGP flap damping values, you define actions by creating a named set of damping parameters and including it in a routing policy with the damping action. For the damping routing policy to work, you also must enable BGP route flap damping.

To configure damping with a policy named dampenpolicy1, perform these steps:

  1. Navigate to the top of the configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 84.
  3. If you are finished configuring the router, commit the configuration.

Table 84: Creating a Policy to Accept and Apply Damping on Routes

Task

J-Web Configuration Editor

CLI Configuration Editor

Navigate to the Policy statement level in the configuration hierarchy.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Policy options, click Configure or Edit.
  3. Next to Policy statement, click Add new entry.

From the [edit] hierarchy level, enter

edit policy-options policy-statement

Create a damping policy and term—for example, dampenpolicy1 and dampenterm1.
  1. In the Policy name box, type dampenpolicy1.
  2. Next to Term, click Add new entry.
  3. In the Term name box, type dampenterm1.

Enter

set dampenpolicy1 term dampenterm1

Specify the routes to dampen and associate each group of routes with a group name. For example:

  • group1—Routes greater than or equal to 172.16.0.0/12
  • group2—Routes greater than or equal to 192.168.0.0/16
  • group3—Routes greater than or equal to 10.0.0.0/8
  1. Next to From, click Configure.
  2. Next to Route filter, click Add new entry.
  3. In the Address box, type 172.16.0.0/12.
  4. In the Damping box, type group1.
  5. From the Modifier list, select Orlonger.
  6. Click OK.

Specify the first routes to dampen:

set from route-filter 172.16.0.0/12 orlonger damping group 1

  1. Next to Route filter, click Add new entry.
  2. In the Address box, type 192.168.0.0/16.
  3. In the Damping box, type group2.
  4. From the Modifier list, select Orlonger.
  5. Click OK.

Specify the next routes to dampen:

set from route-filter 192.168.0.0/16 orlonger

  1. Next to Route filter, click Add new entry.
  2. In the Address box, type 10.0.0.0/8.
  3. In the Damping box, type group3.
  4. From the Modifier list, select Orlonger.
  5. Click OK until you return to the Policy options page.

Specify the last routes to dampen:

set from route-filter 10.0.0.0/8 orlonger

Create three damping parameter groups with different damping actions. For example:

  • group1—Increases the half-life to 30 minutes. All other parameters are left at their default values.
  • group2—Increases the half-life to 40 minutes, decreases the maximum hold-down time for a route to 45 minutes, increases the reuse value to 1000, and reduces the cutoff (suppression) threshold to 400.
  • group3—Disables route damping.

For each damping group:

  1. Next to Damping, click Add new entry.
  2. In the Damping object name box, type the name of a damping group—for example, group1.
  3. In the Half life box, type the half-life duration, in minutes:
    • For group1—30
    • For group2—40
  4. In the Max suppress box, type the maximum hold-down time, in minutes:
    • For group1—60 (the default)
    • For group2—45
  5. In the Reuse box, type the reuse threshold, for this damping group:
    • For group1—750 (the default)
    • For group2—1000
  6. In the Suppress box, type the cutoff threshold, for this damping group:
    • For group1—3000 (the default)
    • For group2—400
  7. To disable damping for the group3 damping group, select the Disable check box.
  8. Click OK when you finish configuring each group.

Create and configure the damping parameter groups:

edit damping group1 half-life 30 max-suppress 60 reuse 750 suppress 3000

edit damping group2 half-life 40 max-suppress 45 reuse 1000 suppress 400

edit damping group3 disable

Navigate to the Bgp level in the configuration hierarchy.
  1. On the main Configuration page next to Protocols, click Configure or Edit.
  2. Next to Bgp, click Configure or Edit.

From the [edit] hierarchy level, enter

edit protocols bgp

Enable damping.
  1. Select the Damping check box.
  2. Click OK.

Enable damping:

set damping

Navigate to the Neighbor level in the configuration hierarchy, for the BGP neighbor to which you want to apply the damping policy—for example, the neighbor at IP address 172.16.15.14.
  1. On the main Configuration page next to Protocols, click Edit.
  2. Next to Bgp, click Edit.
  3. Under Group name, click groupA.
  4. Under Neighbor Address, click 172.16.15.14.

From the [edit] hierarchy level, enter

edit protocols bgp group groupA neighbor 172.16.15.14

Apply the policy as an import policy for the BGP neighbor.

The routing policy is evaluated when routes are imported to the routing table.
  1. Next to Import, click Add new entry.
  2. In the Value box, type the name of the policy.
  3. Click OK.

Apply the policy:

set import dampenpolicy1

You can refer to the same routing policy one or more times in the same or a different import statement.
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