Configuring Neighbor Relationship Flapping Suppression on an OSPF Multi-Area Adjacency Interface

Neighbor relationship flapping suppression can be configured on an OSPF multi-area adjacency interface to delay OSPF neighbor relationship reestablishment or set the link cost to the maximum value in case of neighbor relationship flapping.

Usage Scenario

If an interface carrying OSPF services alternates between Up and Down, OSPF neighbor relationship flapping occurs on the interface. During the flapping, 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 neighbor relationship stability, OSPF services, and other OSPF-dependent services, such as LDP and BGP. OSPF neighbor relationship flapping suppression can address this problem by delaying OSPF neighbor relationship reestablishment or preventing service traffic from passing through flapping links.

The following steps are optional, and choose them as required.

Procedure

Run the system-view command to enter the system view.
To disable the function globally, run the suppress-flapping peer disable command.
Run interface interface-type interface-number
The interface view is displayed.
Run ospf enable [ process-id ] area area-id
OSPF is enabled on the interface.
Run ospf enable multi-area area-id
OSPF is enabled on the multi-area adjacency interface.
(Optional) Run ospf suppress-flapping peer disable multi-area area-id
OSPF neighbor relationship flapping suppression on a multi-area adjacency interface is disabled.

To disable OSPF neighbor relationship flapping suppression from one of the interfaces, run this command.
Run ospf suppress-flapping peer hold-down interval multi-area area-id
The Hold-down mode is configured on a multi-area adjacency interface, and its 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, interfaces prevent neighbor relationship reestablishment during Hold-down suppression, which minimizes LSDB synchronization attempts and packet exchanges.
- Hold-max-cost mode: If the traffic forwarding path changes frequently, interfaces use 65535 (the maximum cost) as the cost of the flapping link during Hold-max-cost suppression, which prevents traffic from passing through the flapping link.
  
  To change the cost used by the Hold-max-cost mode, run the maximum-link-cost cost command.
Flapping suppression can also work first in Hold-down mode and then in Hold-max-cost mode.

To disable the Hold-max-cost mode, run the ospf suppress-flapping peer hold-max-cost disable multi-area command.
Run the ospf suppress-flapping peer { detecting-interval detecting-interval | threshold threshold | resume-interval resume-interval } ^* multi-area area-id command to configure detection parameters for OSPF neighbor relationship flapping suppression on the multi-area adjacency interface.
- Specifies the interval for exiting from OSPF neighbor relationship flapping suppression.
  
  If the interval between two successive neighbor status changes from Full to a non-Full state is longer than resume-interval, the flapping_count is reset.
- If OSPF neighbor relationship flapping suppression works in hold-max-cost mode, resume-interval indicates the duration of this mode.
The value of resume-interval must be greater than that of detecting-interval.
You can configure detection parameters for OSPF neighbor relationship flapping suppression on specific interfaces according to network conditions. However, using the default values of these parameters is recommended.
Run quit
The system view is displayed.
Run quit
The user view is displayed.
Run reset ospf suppress-flapping process-id peer [ interface-name [ all-areas | area area-id ] | interface-type interface-number [ all-areas | areaarea-id ] ] [ notify-peer ]
The OSPF multi-area adjacency interface is configured to exit OSPF neighbor relationship flapping suppression.
The interface exits flapping suppression in the following scenarios:
- The suppression timer expires.
- The corresponding OSPF process is reset.
- An OSPF neighbor is reset using the reset ospf peer command.
- OSPF neighbor relationship flapping suppression is disabled globally using the suppress-flapping peer disable (OSPF) command.
- The reset ospf suppress-flapping peer command is run.
Run commit
The configuration is committed.