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Configuration Guide - IP Unicast Routing

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of IP Unicast Routing, including IP Routing, Static Route, RIP, RIPng, OSPF, OSPFv3, IPv4 IS-IS, IPv6 IS-IS, BGP, Routing Policy, and PBR.
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Configuring Suppression of OSPF Neighbor Relationship Flapping

Configuring Suppression of OSPF Neighbor Relationship Flapping

Context

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. Suppression of OSPF neighbor relationship flapping can address this problem by delaying OSPF neighbor relationship reestablishment or preventing service traffic from passing through flapping links.

Pre-configuration Tasks

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

Procedure

  1. 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 in the OSPF view.

  2. Run interface interface-type interface-number

    The interface view is displayed.

    To disable this function on a specified interface, run the ospf suppress-flapping peer disable command in the interface view.

  3. On an Ethernet interface, run undo portswitch

    The interface is switched to Layer 3 mode.

    By default, an Ethernet interface works in Layer 2 mode.

    The mode switching function takes effect when the interface only has attribute configurations (for example, shutdown and description configurations). Alternatively, if configuration information supported by both Layer 2 and Layer 3 interfaces exists (for example, mode lacp and lacp system-id configurations), no configuration that is not supported after the working mode of the interface is switched can exist. If unsupported configurations exist on the interface, delete the configurations first and then run the undo portswitch command.

    NOTE:

    If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.

  4. 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 prohibit 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 the maximum value 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 work first in Hold-down mode and then in Hold-max-cost mode after the Hold-down mode exits.

    By default, the Hold-down mode is disabled, and 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.

  5. Run ospf suppress-flapping peer { detecting-interval detecting-interval | threshold threshold | resume-interval resume-interval } *

    Detection parameters are configured for suppressing OSPF neighbor relationship flapping.

    • The parameter resume-interval resume-interval specifies the interval for exiting the suppression of OSPF neighbor relationship flapping.

      If the interval between two successive neighbor status changes from Full to ExStart or Down is longer than resume-interval, the flapping_count is reset to 0.

    • If flapping suppression works in Hold-max-cost mode, resume-interval indicates the duration of this mode.
    NOTE:

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

    Flapping suppression detection parameters can be set based on the network requirements on a specified interface. By default, the detection interval of flapping suppression is 60s, the suppression threshold is 10, and the interval for exiting suppression is 120s. Default values are recommended for the detection parameters.

  6. Run commit

    The configuration is committed.

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.

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Updated: 2019-04-20

Document ID: EDOC1100074760

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