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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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Summary of OSPF Configuration Tasks

Summary of OSPF Configuration Tasks

After basic OSPF functions are configured, you can build a basic OSPF network. On the basic OSPF network, you can configure other OSPF functions as required.

Table 5-19 describes the OSPF configuration tasks.

Table 5-19 OSPF configuration tasks

Scenario

Description

Task

Configuring Basic OSPF Functions

The configuration of basic OSPF functions is the foundation of the OSPF network and the precondition for other OSPF functions.

Configuring Basic OSPF Functions

Setting Session Parameters for OSPF Neighbor Relationships

Configuring OSPF Attributes in Different Types of Networks

Configuring OSPF Areas

  • In a stub area, the area border router (ABR) does not transmit learned autonomous system (AS) external routes. This implementation reduces entries in the routing tables on ABRs in stub areas and the amount of routing information to be transmitted.

  • An NSSA is a new type of OSPF area. Neither the NSSA nor the stub area transmits routes learned from other areas in the AS on which it resides. Different from the stub area, the NSSA allows AS external routes to be imported and forwarded in the entire AS.

Configuring OSPF Stub Areas

Configuring OSPF NSSA

Adjusting OSPF Route Selection

To meet various user requirements, you can adjust OSPF parameters to flexibly control OSPF routing.

Adjusting OSPF Route Selection

Controlling OSPF Routing Information

To meet network requirements, you can configure different parameters to accurately control the advertising and receiving of OSPF routes.

Controlling OSPF Routing Information

Controlling the Convergence Speed of OSPF Routes

To enable OSPF to quickly detect changes in the network topology, you can speed up OSPF route convergence. To decrease the impact of route flapping on the network and relieve loads on devices, you can lower the convergence speed of OSPF routes.

Configuring OSPF Fast Convergence

Improving the Reliability of an OSPF Network

  • OSPF IP FRR pre-computes a backup link by using the Loop-Free Alternate (LFA) algorithm, and then adds the backup link and the primary link to the forwarding table. In the case of failures, OSPF IP FRR can fast switch traffic to the backup link before routes on the control plane converge. This prevents traffic interruption, protects traffic, and improves reliability of an OSPF network.

  • By default, the interval for OSPF to send Hello packets is 10 seconds on broadcast networks; on NBMA networks, the interval for sending Hello packets is 30 seconds. The interval for declaring a neighbor Down, that is, the dead time after which the neighbor relationship becomes invalid, is four times the interval for sending Hello packets. If the router does not receive a Hello packet from its neighbor within the dead time, the router deletes the neighbor. That is, the router detects neighbor faults at the second level. This causes a large number of packets to be lost on a high-speed network.

    Bidirectional Forwarding Detection (BFD) is introduced to solve the preceding problem in the existing detection mechanism. BFD ensures that the detection interval is reduced to the millisecond level. Instead of replacing the Hello mechanism of OSPF, BFD works with OSPF to fast detect the adjacency fault. In addition, BFD instructs OSPF to recalculate corresponding routes to ensure correct packet forwarding.

  • When a router restarts or performs an active/standby switchover, it directly ages all routing entries in the Forward Information Base (FIB) table. This results in route interruption. In addition, neighboring routers remove this router from the neighbor list, and notify other routers. This causes the re-calculation of SPF. If this router recovers within a few seconds, the neighbor relationship becomes unstable. This results in route flapping.

    After being enabled with OSPF Graceful Restart (GR), a router can ensure continuous packet forwarding in the event of a restart caused by an abnormality. In such a case, route flapping is avoided during the short restart of the router.

Configuring OSPF IP FRR

Configuring BFD for OSPF

Configuring OSPF GR

Improving the Stability of an OSPF Network

You can improve the stability of the OSPF network to reduce route flapping on the OSPF network and enable the device to work in a normal state for a long time.

Improving the Stability of an OSPF Network

Improving the Security of an OSPF Network

In a network demanding high security, you can configure OSPF authentication and adopt the GTSM mechanism to improve the security of the OSPF network.

Improving the Security of an OSPF Network

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Updated: 2019-05-20

Document ID: EDOC1100034072

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