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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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Configuring OSPF to Advertise the Default Route to the OSPF Area

Configuring OSPF to Advertise the Default Route to the OSPF Area

Context

Multiple routers often reside on the area border and AS border of an OSPF network for next-hop backup or traffic load balancing. A default route can be configured to reduce routing entries and improve resource usage on the OSPF network.

The default route is generally applied to the following scenarios:

  1. An ABR in an area advertises Type 3 LSAs carrying the default route within the area. routers in the area use the received default route to forward inter-area packets.
  2. An ASBR in an AS advertises Type 5 or Type 7 LSAs carrying the default route within the AS. routers in the AS use the received default route to forward AS external packets.

When no exactly matched route is discovered, the router can forward packets through the default route.

The preference of the default route in Type 3 LSAs is higher than that of the route in Type 5 or Type 7 LSAs.

The advertising mode of the default route is determined by the type of the area to which the default route is imported, as shown in Table 5-22.

Table 5-22 Default route advertising mode

Area Type

Generated By

Advertised By

LSA Type

Flooding Area

Common area

The default-route-advertise command

ASBR

Type 5 LSA

Common area

Stub area

Automatically

ABR

Type 3 LSA

Stub area

NSSA

The nssa [ default-route-advertise ] command

ASBR

Type 7 LSA

NSSA

Totally NSSA

Automatically

ABR

Type 3 LSA

NSSA

Perform the following steps on the ASBR running OSPF.

Procedure

  • Configuring OSPF to advertise the default route to the OSPF area
    1. Run system-view

      The system view is displayed.

    2. Run ospf [ process-id ]

      The OSPF process view is displayed.

    3. Run the following commands as required:

      • Run default-route-advertise [ [ always | permit-calculate-other ] | cost cost | type type | route-policy route-policy-name [ match-any ] ] *

        OSPF is configured to advertise the default route to the OSPF area.

        • always indicates that an LSA describing the default route is generated and then advertised regardless of whether there are active default routes of other OSPF processes in the routing table of the local device.
        • permit-calculate-other indicates that the local router is still allowed to calculate the default routes advertised by other routers after adverting its default route.
        • route-policy route-policy-name indicates that the local device advertises default routes according to the parameters of the configured routing policy when there are matched default routing entries generated by other OSPF processes.
      • Run default-route-advertise summary cost cost

        The default cost of a Type 3 summary LSA is set.

        Before selecting the preceding parameters, you need to configure VPN. Otherwise, this command cannot be run.

      NOTE:
      • An ASE LSA that describes the default route is generated and then advertised only when there are active default routes of other OSPF processes in the routing table of the local device.
      • Before advertising a default route, OSPF compares the preferences of default routes. Therefore, if a static default route is configured on an OSPF router, to add the default route advertised by OSPF to the current routing table, ensure that the preference of the configured static default route is lower than that of the default route advertised by OSPF.

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Updated: 2019-05-20

Document ID: EDOC1100034072

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