No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

Configuration Guide - IP Routing 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Configuration Guide - IP Routing
Rate and give feedback:
Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Configuring an NSSA

Configuring an NSSA

Configuring a non-backbone area on the border of an AS as an NSSA can reduce entries in the routing table and the amount of routing information to be transmitted. This section describes how to set the cost of the default route to an NSSA and adjust the selection of the default route.

Usage Scenario

An excessive number of entries in a routing table wastes network resources and causes high CPU usage. To reduce entries in a routing table, configure a non-backbone area on the border of an AS as a stub area or an NSSA to reduce the amount of routing information to be transmitted. For details on how to configure an OSPF stub area, see Configuring an OSPF Stub Area.

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 where it resides. Different from the stub area, the NSSA allows AS external routes to be imported and forwarded in the entire AS.

If you want to import AS external routes to an area and prevent these routes from consuming resources, configure the area as an NSSA.

Type 7 link state advertisements (LSAs) are used to carry imported AS external routes in the NSSA. Type 7 LSAs are generated by ASBRs of NSSAs and flooded only in the NSSAs where ASBRs reside. The ABR in an NSSA selects Type 7 LSAs from the received LSAs and translates them into Type 5 LSAs to advertise AS external routes to the other areas over the OSPF network.

NOTE:
  • A Type 7 LSA was introduced to support NSSAs and describe imported external routes.
  • Type 7 LSAs can be used to carry default route to transmit traffic to other ASs.

To configure an area as an NSSA, configure NSSA attributes on all the NEs in this area.

Pre-configuration Tasks

Before configuring an NSSA, complete the following tasks:

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run ospf [ process-id ]

    The OSPF process view is displayed.

  3. Run area area-id

    The OSPF area view is displayed.

  4. Run nssa [ default-route-advertise [ backbone-peer-ignore ] | no-import-route | no-summary | set-n-bit | suppress-forwarding-address | translator-always | translator-interval interval-value | zero-address-forwarding ] *

    The area is configured as an NSSA.

    NOTE:
    • NSSA attributes must be configured on all NEs in the NSSA using the nssa command.
    • Configuring or deleting NSSA attributes may trigger routing update in the area and disconnection from neighbors. The NSSA attributes can be reconfigured or re-canceled only after the routing update is complete.

    The nssa command is applicable to the following scenarios:

    • Default Type 7 LSAs are generated and advertised to an NSSA.

      1. OSPF neighbor relationships that are in the Full state and interfaces that are Up exist in the backbone area.
      2. The default-route-advertise parameter is configured.
      3. Other default routes destined for 0.0.0.0 exist in the local routing table.

      If condition 1 is met, ABRs generate default Type 7 LSAs and advertise them to the NSSA. If conditions 2 and 3 are met, ASBRs generate default Type 7 LSAs and advertise them to the NSSA.

    • The parameter backbone-peer-ignore is used to prevent the ABR from checking the neighbor status when the ABR generates default Type 7 LSAs and advertises them to the NSSA. Specifically, the ABR generates default Type 7 LSAs and advertises them to the NSSA as long as an interface that is Up exist in the backbone area.

    • An ASBR also functions as an ABR, and the no-import-route parameter is configured to prevent external routes imported using the import-route command from being advertised to the NSSA.
    • The no-summary parameter is configured on an ABR to reduce the number of LSAs to be transmitted to the NSSA, which prevents the ABR from transmitting Type 3 LSAs to the NSSA.
      NOTE:
      After the nssa default-route-advertise backbone-peer-ignore no-summary command is run, the ABR generates default Type 7 and Type 3 LSAs as long as an interface that is Up exist in the backbone area. The default Type 3 LSAs preferentially take effect.
    • After the set-n-bit parameter is configured, the N-bit is set in the database description (DD) packets during the synchronization between the NE and neighboring NEs.
    • The suppress-forwarding-address parameter sets the forwarding address (FA) of the Type 5 LSAs translated from Type 7 LSAs by the NSSA ABR to 0.0.0.0.
    • If multiple ABRs are deployed in the NSSA, the system automatically selects an ABR (the NE with the largest router ID) as a translator to convert Type 7 LSAs into Type 5 LSAs. You can configure the translator-always parameter on an ABR to specify the ABR as an all-the-time translator. To specify two ABRs for load balancing, configure the translator-always parameter on the chosen ABRs to specify the ABRs as all-the-time translators. You can use this command to pre-configure a fixed translator to prevent LSA flooding caused by translator role changes.
    • The translator-interval parameter is used to ensure uninterrupted services when translator roles change. The value of interval-value must be greater than the flooding interval.
    • The zero-address-forwarding parameter is used to set the FA of the generated NSSA LSAs to 0.0.0.0 when external routes are imported to the ABR in an NSSA.

  5. (Optional) Run default-cost cost

    The cost of the default route carried in Type 3 LSAs that are transmitted by the ABR to the NSSA is set.

    To ensure the reachability of AS external routes, the ABR in the NSSA generates a default route and advertises it to other NEs in the NSSA.

    By default, the cost of the default route that is sent by the ABR to the NSSA is 1.

  6. Run commit

    The configuration is committed.

Checking the Configurations

Run either of the following commands to check LSDB information:

  • display ospf [ process-id ] lsdb [ brief ]

  • display ospf [ process-id ] lsdb [ router | network | summary | asbr | ase | nssa | opaque-link | opaque-area ] [ link-state-id ] [ originate-router [ advertising-router-id ] | self-originate ]

Run either of the following commands to check routing table information:

  • display ospf [ process-id ] routing [ ip-address [ mask | mask-length ] ] [ interface interface-type interface-number ] [ nexthop nexthop-address ]

  • display ospf [ process-id ] routing router-id [ router-id ]

Run the display ospf [ process-id ] interface [ all | no-peer | interface-type interface-number ] [ verbose ] command to check OSPF interface information.

Run the display ospf routing command before configuring an NSSA.

# Check the routing table on Device A.

<HUAWEI> display ospf routing
          OSPF Process 1 with Router ID 1.1.1.1
                   Routing Tables

 Routing for Network
 Destination        Cost  Type       NextHop         AdvRouter     Area
 192.168.3.0/24     2     Inter-area 192.168.0.1     1.1.1.1       0.0.0.0
 192.168.4.0/24     2     Inter-area 192.168.2.1     2.2.2.2       0.0.0.0
 192.168.0.0/24     1     Stub       192.168.0.2     3.3.3.3       0.0.0.0
 192.168.1.0/24     2     Inter-area 192.168.2.1     2.2.2.2       0.0.0.0
 192.168.1.0/24     2     Inter-area 192.168.0.1     1.1.1.1       0.0.0.0
 192.168.2.0/24     1     Stub       192.168.2.2     3.3.3.3       0.0.0.0

 Routing for ASEs
 Destination      Cost      Type       Tag    NextHop         AdvRouter
 100.0.0.0/8      1         Type2      1      192.168.0.1     2.2.2.2

 Total Nets: 7
 Intra Area: 2  Inter Area: 4  ASE: 1  NSSA: 0

Run the display ospf routing command after configuring an NSSA.

# Check the routing table on Device A.

<HUAWEI> display ospf routing
          OSPF Process 1 with Router ID 1.1.1.1
                   Routing Tables

 Routing for Network
 Destination        Cost  Type       NextHop         AdvRouter     Area
 192.168.0.0/24     1     Stub       192.168.0.2     3.3.3.3       0.0.0.0
 192.168.2.0/24     1     Stub       192.168.2.2     3.3.3.3       0.0.0.0

 Routing for NSSAs
 Destination      Cost      Type       Tag    NextHop         AdvRouter
 100.0.0.0/8      1         Type2      1      192.168.0.1     2.2.2.2

 Total Nets: 7
 Intra Area: 2  Inter Area: 4  ASE: 0  NSSA: 1

By comparing the routing tables before and after an NSSA is configured, you can reach the following conclusions:

  • After an area is configured as an NSSA, the number of entries in the routing table is reduced.
  • AS external routes are imported to the NSSA.
Translation
Download
Updated: 2019-01-14

Document ID: EDOC1100058916

Views: 37730

Downloads: 57

Average rating:
This Document Applies to these Products
Related Version
Related Documents
Share
Previous Next