dampening
Function
The dampening command enables BGP route flap suppression and modifies BGP route flap suppression parameters.
The undo dampening command restores the default configuration.
By default, BGP route flap suppression is disabled.
Format
dampening [ ibgp ] [ half-life-reach reuse suppress ceiling | route-policy route-policy-name ] *
undo dampening [ ibgp ]
Parameters
| Parameter | Description | Value |
|---|---|---|
| half-life-reach | Specifies the half life of a reachable route. | The value is an integer that ranges from 1 to 45, in minutes. The default value is 15. |
| reuse | Specifies the threshold for the route to be unsuppressed. If the penalty of the route falls below the threshold, the route is reused. | The value is an integer that ranges from 1 to 20000. The default value is 750. |
| suppress | Specifies the threshold for the route to be suppressed. If the penalty value of the route exceeds the threshold, the route is not used. | The value is an integer that ranges from 1 to 20000, which must be greater than the value of reuse. The default value is 2000. |
| ceiling | Specifies the penalty ceiling. | The value is an integer that ranges from 1001 to 20000. The configured value must be greater than that of suppress. The default value is 16000. |
| route-policy route-policy-name | Specifies the name of a route-policy. | The name is a string of 1 to 40 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string. |
| ibgp | Specifies the route type as IBGP route. If this parameter
is not specified, the route type is EBGP route. NOTE:
This parameter takes effect only in the BGP-VPNv4 address family view. |
- |
Views
BGP view, BGP-IPv4 unicast address family view, BGP-IPv6 unicast address family view, BGP-VPN instance IPv4 address family view, BGP-VPN instance IPv6 address family view, BGP-IPv4 multicast address family view, BGP-VPNv4 address family view
Usage Guidelines
Usage Scenario
BGP route flap dampening measures the stability of a route by using a penalty value. The greater the penalty value, the less stable the route. Each time route flapping occurs, that is, when the switch receives a Withdraw packet or an Update packet for a route, BGP adds a certain penalty value (1000) for the route.
When the penalty value of the route exceeds the suppression threshold, the route is suppressed. The switch does not add the route to the IP routing table or advertise any Update packet to other BGP peers. If the route is marked with the d flag, the last packet received by the switch is an Update packet; if the route is marked with the h flag, the last packet received by the switch is a Withdraw packet. After the penalty value reaches a certain limit, it does not increase any more. The limit is called the penalty ceiling.
After the route is suppressed for a certain period, the penalty value is reduced by half. If the penalty value of a route marked with the d flag decreases to the reuse threshold, the d flag is removed, and the route becomes available and is selected preferentially. After that, the route can be added to the IP routing table and used to send Update packets to other BGP peers. If the penalty value of a route marked with the h flag decreases to 0, the route is deleted from the BGP routing table.
You can run the display bgp routing-table label command to check the d flag and h flag indicating the routes that have been dampened and were dampened respectively.
Precautions
If the dampening command is run multiple times, the latest configuration overrides the previous one.
After the dampening command is run, the system suppresses unstable routes. This means that the system does not add unstable routes to the BGP routing table or advertise them to other BGP peers.
Note the following items when configuring BGP route flap dampening:
The value of suppress must be greater than that of reuse and smaller than that of ceiling.
If MaxSuppressTime obtained by using the formula of MaxSuppressTime = half-life-reach x 60 x (ln(ceiling/reuse)/ln(2)) is smaller than 1, suppression cannot be performed. You need to ensure that the value of MaxSuppressTime is equal to or greater than 1. This means that the value of ceiling/reuse must be great enough.
The dampening command is valid only for EBGP routes.
Creating a route-policy before it is referenced is recommended. By default, nonexistent route-policies cannot be referenced using the command. If the route-policy nonexistent-config-check disable command is run in the system view and a nonexistent route-policy is referenced using the current command, the configured dampening parameters apply to all routes; if no dampening parameters are configured, the default dampening parameters apply to the routes.