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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 OSPF to Import External Routes

Configuring OSPF to Import External Routes

Context

OSPF can ensure loop-free intra-area and inter-area routes; however, OSPF cannot protect external routes against loops. Therefore, when configuring OSPF to import external routes, you need to avoid the loops caused by manual configurations.

Perform the following steps on a switch that functions as an ASBR running OSPF:

Procedure

  • Configuring OSPF to import routes discovered by other protocols
    1. Run system-view

      The system view is displayed.

    2. Run ospf [ process-id ]

      The OSPF process view is displayed.

    3. Run import-route { bgp [ permit-ibgp ] | direct | rip [ process-id-rip ] | static | isis [ process-id-isis ] | ospf [ process-id-ospf ] } [ cost cost | route-policy route-policy-name | tag tag | type type ] *

      OSPF is configured to import routes discovered by other protocols.

    4. Run commit

      The configuration is committed.

  • Setting parameters for OSPF to import routes
    1. Run system-view

      The system view is displayed.

    2. Run ospf [ process-id ]

      The OSPF process view is displayed.

    3. Run default { cost { cost-value | inherit-metric } | tag tag | type type } *

      The default parameter values (route cost, tag, and type) are set for OSPF to import routes.

      • The parameter cost cost-value specifies the default cost of external routes imported by OSPF.
      • The parameter inherit-metric indicates that the cost carried in an imported route itself is inherited. If the cost is not specified in an imported route, the default cost set using the default command is used as the cost of the imported route.

      When OSPF is configured to import external routes, you can assign default values to some additional parameters, such as route cost, tag, and type. The route tag identifies protocol-related information. For example, it can be used to differentiate AS numbers when OSPF receives BGP routes.

      By default, the cost of external routes imported by OSPF is 1; the type of imported external routes is Type 2; the tag value is 1.
      NOTE:
      You can run one of the following commands, listed in descending order of priority, to set the cost of imported external routes:
      • Run the apply cost command in the route-policy view to set the cost of imported external routes.
      • Run the import-route command in the OSPF view to set the cost of imported external routes.
      • Run the default command to set the default cost of imported external routes.

    4. Run import-route limit limit-number [ threshold-alarm { upper-limit upper-limit-value | lower-limit lower-limit-value } * ]

      A limit is configured on the number of LSAs that can be generated by an OSPF process for imported external routes.

      By default, the number of LSAs generated by an OSPF process for imported external routes is not limited.

      If OSPF imports a large number of external routes and advertises them to a device with a smaller routing table capacity, the device may restart unexpectedly. To address this problem, run the import-route limit command to configure a limit on the number of LSAs generated when an OSPF process imports external routes.

      Check the overload status based on the value of the Current status field in the display ospf brief command output.
      • Normal: The number of LSAs generated when an OSPF process imports external routes is less than or equal to the lower alarm threshold (in percentage) multiplied by the maximum number allowed.
      • Approach limit: The number of LSAs generated when an OSPF process imports external routes is approaching (reaching or exceeding 90% of) the upper alarm threshold.
      • Exceed limit: The number of LSAs generated when an OSPF process imports external routes has reached or exceeded the maximum number allowed.

      Ensure that upper-limit-value is greater than or equal to lower-limit-value.

    5. Run lsdb-overflow-limit number

      The maximum number of external routes supported in an OSPF LSDB is set.

      By default, the maximum number of external routes supported in an OSPF LSDB is not limited.

      The lsdb-overflow-limit command is run to ensure that the number of routes is limited within a proper range. If the number of external routes imported by OSPF exceeds the configured maximum number, the device deletes self-generated non-default external routes to ensure the proper forwarding of other external routes.

    6. Run commit

      The configuration is committed.

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Updated: 2019-04-20

Document ID: EDOC1100074760

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