Configuring OSPF Neighbor Relationship Flapping Suppression

Applicable Environment

If an interface carrying OSPF services frequently alternates between Up and Down, the OSPF neighbor relationship flaps on the interface. In this case, OSPF frequently sends Hello packets to reestablish the neighbor relationship, synchronizes LSDBs, and recalculates routes. In this process, a large number of packets are exchanged, adversely affecting stability of existing neighbor relationships, OSPF services, and other OSPF-dependent services, such as LDP and BGP. To address this problem, OSPF implements suppression of neighbor relationship flapping to delay OSPF neighbor relationship reestablishment or prevent service traffic from passing through flapping links.

The following steps are optional.

Pre-configuration Tasks

Before configuring OSPF neighbor relationship flapping suppression, complete the following tasks:

Configure IP addresses for interfaces to ensure that neighboring nodes are reachable at the network layer.
Configuring Basic OSPF Functions

Procedure

Run system-view

The system view is displayed.

By default, suppression of OSPF neighbor relationship flapping is enabled globally. To disable this function globally, run the suppress-flapping peer disable command.
Run interface interface-type interface-number

The interface view is displayed.

By default, suppression of OSPF neighbor relationship flapping is enabled on all interfaces in the same OSPF process. To disable this function on an interface, run the ospf suppress-flapping peer disable command.
Run ospf suppress-flapping peer hold-down interval

The Hold-down mode of flapping suppression is configured, and the suppression duration is set.

Flapping suppression works in either Hold-down or Hold-max-cost mode.
- Hold-down mode: In the case of frequent flooding and topology changes during neighbor relationship establishment in an interface, the interface prevents the reestablishment of the neighbor relationship, which minimizes LSDB synchronization attempts and packet exchanges.
- Hold-max-cost mode: If the traffic forwarding path changes frequently, the interface uses the maximum value 65535 as the cost of the flapping link, which prevents traffic from passing through the flapping link.
Flapping suppression can also work first in Hold-down mode and then in Hold-max-cost mode after the Hold-down mode exits.

By default, only the Hold-max-cost mode is enabled.

To disable the Hold-max-cost mode, run the ospf suppress-flapping peer hold-max-cost disable command.
Run ospf suppress-flapping peer { detecting-interval detecting-interval | threshold threshold | resume-interval resume-interval } ^*

Detection parameters are configured for OSPF neighbor relationship flapping suppression.

Each OSPF interface with OSPF neighbor relationship flapping suppression enabled starts a flapping counter. If the interval between two successive status changes of a neighbor from Full to a non-Full state is shorter than detecting-interval, a valid flapping_event is recorded and the flapping_count increments by 1. When the flapping_count reaches or exceeds threshold, flapping suppression takes effect. If the interval between two successive status changes of a neighbor from Full to a non-Full state is longer than resume-interval, the flapping_count is reset.

The value of resume-interval must be greater than that of detecting-interval.

By default, the value of detecting-interval is 60s, the value threshold is 10, and the value of resume-interval is 120s. Default values of the detection parameters are recommended.
Run quit

The system view is displayed.
Run quit

The user view is displayed.
Run reset ospf process-id suppress-flapping peer [ interface-type interface-number ] [ notify-peer ]

The interface is forced to exit the suppression of OSPF neighbor relationship flapping.
An interface exits flapping suppression in any of the following scenarios:
- The suppression timer expires.
- The corresponding OSPF process is reset.
- Suppression of OSPF neighbor relationship flapping is disabled globally using the suppress-flapping peer disable command in the OSPF view.
- The reset ospf suppress-flapping peer command is run.

Verifying the Configuration

Run the display ospf [ process-id ] interface interface-type interface-number verbose command to check the status of OSPF neighbor relationship flapping suppression.

<HUAWEI> display ospf interface vlanif 100 verbose

           OSPF Process 1 with Router ID 10.1.1.2
                  Interfaces
                  
 Interface: 10.0.0.2 (VLANIF100)
 Cost: 1       State: DR        Type: Broadcast    MTU: 1500
 Priority: 1
 Designated Router: 10.0.0.2
 Backup Designated Router: 10.0.0.1
 Timers: Hello 10 , Dead 40 , Poll  120 , Retransmit 5 , Transmit Delay 1
  IO Statistics
             Type        Input     Output
            Hello       161367      10436
 DB Description             18         18
 Link-State Req              5          6
 Link-State Update       203780       210
 Link-State Ack          90411        276
 ALLSPF GROUP
 ALLDR GROUP
 OpaqueId: 1   PrevState: BDR
 Effective cost: 1, enabled by OSPF Protocol.
 Suppress flapping peer: enable(flapping-count: 0, threshold: 20)

In the command output, Suppress flapping peer contains the information indicating that flapping suppression is enabled.