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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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OSPF Database Overflow

OSPF Database Overflow

Definition

OSPF requires that routers in the same area have the same Link-State Database (LSDB).

With the continuous increase in routes on the network, some routers fail to carry the additional routing information because of limited system resources. This situation is called OSPF database overflow.

Purpose

You can configure stub areas or NSSAs to solve the problem of the continuous increase in routing information that causes the exhaustion of system resources of routers. However, configuring stub areas or NSSAs cannot solve the problem when the unexpected increase in dynamic routes causes database overflow. Setting the maximum number of external LSAs in the LSDB can dynamically limit the LSDB capacity, to avoid the problems caused by database overflow.

Principle

To prevent database overflow, you can set the maximum number of non-default external routes on a router.

All routers on the OSPF network must be set with the same upper limit. If the number of external routes on a router reaches the upper limit, the router enters the Overflow state and starts an overflow timer. The router automatically exits from the overflow state after the timer expires. By default, it is 5 seconds.

Table 5-17 OSPF database overflow

Overflow Phase

OSPF Processing

Entering overflow state

A router deletes all non-default external routes that are generated.

Staying in overflow state

  • Router does not generate non-default external routes.
  • Router discards the newly received, non-default external routes, and does not reply with an LSAck packet.
  • When the overflow timer expires, the router checks whether the number of external routes still exceeds the upper limit.
    • If so, the router restarts the timer.
    • If not, the router exits from overflow state.

Exiting from the overflow state

  • Router deletes the overflow timer.
  • Router generates non-default routes.
  • Router learns the newly received non-default routes, and replies with an LSAck packet.
  • Router prepares to enter Overflow state for the next time it occurs.
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Updated: 2019-05-20

Document ID: EDOC1100034072

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