Configuring OSPF Neighbor Relationship Flapping Suppression

OSPF neighbor relationship flapping suppression works by delaying OSPF neighbor relationship reestablishment or setting the link cost to the maximum value.

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, choose them as required.

Pre-configuration Tasks

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

Configure an IP address for each interface to ensure that neighboring routers are reachable at the network layer.
Configure basic OSPF functions

Procedure

Run:
```
system-view
```
The system view is displayed.

By default, OSPF neighbor relationship flapping suppression 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, OSPF neighbor relationship flapping suppression is enabled on all interfaces in the same OSPF process. To disable the function from one of the interfaces, run the ospf suppress-flapping peer disable command.
Run:
```
ospf suppress-flapping peer hold-down interval
```
The Hold-down mode is configured, 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 as the cost of the flapping link during Hold-max-cost suppression, 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.

By default, the Hold-max-cost mode takes effect.

To set duration for the Hold-max-cost mode or disable this 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 on which OSPF neighbor relationship flapping suppression is enabled starts a flapping counter. If the interval between two successive neighbor status changes from Full to a non-Full state is shorter than detecting-interval, a valid flapping_event is recorded, and the flapping_count increases by 1. When the flapping_count reaches or exceeds threshold, flapping suppression takes effect. 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.

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

By default, the detection interval of OSPF neighbor relationship flapping suppression is 60s, the suppression threshold is 10, and the interval for exiting from suppression is 120s. Using the default detection parameters is 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 ]
```
Interfaces are forced to exit from OSPF neighbor relationship flapping suppression.
Interfaces exit from flapping suppression in the following scenarios:
- The suppression timer expires.
- The corresponding OSPF process is reset.
- OSPF neighbor relationship flapping suppression is disabled globally using the suppress-flapping peer disable(OSPF) command in the OSPF view.
- The reset ospf suppress-flapping peer command is run.

Checking the Configurations

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

<sysname> display ospf interface GigabitEthernet 0/0/0 verbose

           OSPF Process 1 with Router ID 1.1.1.2
                  Interfaces
                  
 Interface: 10.0.0.2 (GigabitEthernet 0/0/0)
 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.
 Link quality adjust cost: No, link quality: 0x0(GOOD).
Support PST: YES    Support Remote LFA: YES
Suppress flapping peer: enable(flapping-count: 0, threshold: 20)

Suppress flapping peer in the command output indicates the current suppression mode (Hold-down), time when the flapping suppression started, and the remaining time of the flapping suppression.