Configuring IS-IS Neighbor Relationship Flapping Suppression

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

Usage Scenario

If an interface carrying IS-IS services alternates between Up and Down, IS-IS neighbor relationship flapping occurs on the interface. During the flapping, IS-IS reestablishes the neighbor relationship and recalculates routes. In this process, a large number of packets are exchanged, adversely affecting neighbor relationship stability, IS-IS services, and other IS-IS-dependent services, such as LDP and BGP. IS-IS neighbor relationship flapping suppression can address this problem by delaying IS-IS 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 IS-IS 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.
Configuring Basic IPv4 IS-IS Functions.

Procedure

Run system-view
The system view is displayed.

To disable IS-IS neighbor relationship flapping suppression globally, run the suppress-flapping peer disable command.
Run interface interfaceType interfaceNum
The interface view is displayed.

To disable IS-IS neighbor relationship flapping suppression from one of the interfaces, run the isis suppress-flapping peer disable command.
Run isis 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 synchronization attempts and packet exchanges.
- Hold-max-cost mode: If the traffic forwarding path changes frequently, interfaces use the maximum value (16777214 for the wide mode and 63 for the narrow mode) 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.

To disable this mode, run the isis suppress-flapping peer hold-max-cost disable command.
Run isis suppress-flapping peer { detecting-interval detecting-interval | threshold threshold | resume-interval resume-interval } ^*
Detection parameters are configured for IS-IS neighbor relationship flapping suppression.

Each IS-IS interface on which IS-IS 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.

Using the default detection parameters is recommended.
Run quit
The system view is displayed.
Run quit
The user view is displayed.
Run reset isis process-id suppress-flapping peer [ interface { interface-name | interfaceType interfaceNum } ] [ notify-peer ]
Interfaces are forced to exit from IS-IS neighbor relationship flapping suppression.
Interfaces exit from flapping suppression in the following scenarios:
- The suppression timer expires.
- The corresponding IS-IS process is reset.
- An IS-IS neighbor is reset using the reset isis peer command.
- IS-IS neighbor relationship flapping suppression is disabled globally using the suppress-flapping peer disable command in the IS-IS view.
- The reset isis suppress-flapping peer command is run.
- Suppression is aborted forcibly using the reset isis process-id suppress-flapping peer [ interface interface-type interface-number ] notify-peer command on the remote device.
Run commit
The configuration is committed.

Checking the Configurations

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