nssa (OSPFv3 area view)

Function

The nssa command configures an NSSA.

The undo nssa command restores an OSPFv3 NSSA to a common OSPFv3 area.

By default, no OSPFv3 area is configured as an NSSA.

Format

nssa [ { default-route-advertise [ backbone-peer-ignore | cost cost-value | tag tag-value | type type-value ] ^* } | no-import-route | no-summary | set-n-bit | translator-always | translator-interval interval-value | suppress-forwarding-address ] ^*

undo nssa

Parameters

Parameter	Description	Value
default-route-advertise	Generates default Type-7 LSAs on the ASBR and then advertises them to the NSSA. The ABR generates a default NSSA LSA (Type7 LSA) automatically and advertises it in the NSSA.	-
backbone-peer-ignore	Prevents an ABR from checking the neighbor status in the backbone area. Specifically, the ABR generates default Type 7 LSAs and advertises them to the NSSA as long as an interface is up in the backbone area.	-
cost cost-value	Specifies the default cost of Type 7 LSAs.	The value is an integer ranging from 1 to 16777214. The default value is 1.
tag tag-value	Specifies the tag value of the OSPFv3 route imported to an NSSA.	The value is an integer ranging from 0 to 4294967295. The default value is 0.
type type-value	Specifies the default type of Type 5 LSAs.	The value can be 1 or 2. 1: Type 1 external route 2: Type 2 external route The default value is 2.
no-import-route	Indicates that no external routes are imported to NSSAs.	-
no-summary	Disables ABRs from sending summary LSAs to NSSAs.	-
set-n-bit	Indicates that the N-bit is set in DD packets.	-
translator-always	Specifies the ABR in an NSSA as the translator. Multiple ABRs in an NSSA can be configured as translators.	-
translator-interval interval-value	Specifies the timeout period of a translator.	The value is an integer ranging from 1 to 120, in seconds. The default value is 40 seconds.
suppress-forwarding-address	Indicates that no forwarding address (FA) is set for Type 5 LSAs that are converted from Type 7 LSAs.	-

Views

OSPFv3 area view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ospf	write

Usage Guidelines

Usage Scenario

An NSSA is configured in the scenario where AS external routes are to be imported but not forwarded to save system resources. AS external routes can be imported to an NSSA and transmitted to the entire NSSA.

All devices in the NSSA must be configured with NSSA attributes using the nssa command. The nssa command is applicable to the following scenarios:

The keyword default-route-advertise is used to generate default Type 7 LSAs. Regardless of whether there is route ::/0 in the routing table on an ABR, a Type 7 LSA default route is generated. A Type 7 LSA default route can be generated only when there is route ::/0 in the routing table on an ASBR.
If an ASBR also functions as an ABR, setting no-import-route prevents external routes imported using the import-route command from being advertised to the NSSA.
To reduce the number of LSAs that are transmitted to the NSSA, set no-summary on an ABR to prevent the ABR from transmitting Type 3 LSAs to the NSSA.
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 is up in the backbone area. The default Type3 LSAs preferentially take effect.
If set-n-bit is set, the DD packets sent by the device carry the N-bit being 1.
If multiple ABRs are deployed in the NSSA, the system automatically selects an ABR (generally the device with the largest router ID) as a translator to convert Type 7 LSAs into Type 5 LSAs. You can also set translator-always on an ABR to specify the ABR as an all-the-time translator. To specify two ABRs for load balancing, configure translator-always on two 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.
translator-interval is used to ensure uninterrupted services when translator roles change. The value must be greater than the flooding period.
You can configure suppress-forwarding-address to disable converted Type 5 LSAs from inheriting the FA of Type 7 LSAs.

Configuration Impact

By default, if backbone-peer-ignore is not configured, the ABR advertises the default route only when a neighbor is in the Full state.

Configuring or deleting NSSA attributes may trigger routing updates in the area. A second configuration of NSSA attributes can be implemented or canceled only after a routing update is complete.

Precautions

When the last ordinary area (other than a stub area or NSSA) in an OSPF process is deleted, useless Type 5 LSAs originated by the local device in the area will be deleted immediately. The local device still reserves useless Type 5 LSAs received from other devices. These useless Type 5 LSAs will not be deleted until the aging time reaches 3600s.

Example

# Configure area 1 as an NSSA.

<HUAWEI> system-view
[~HUAWEI] ospfv3 1
[*HUAWEI-ospfv3-1] area 1
[*HUAWEI-ospfv3-1-area-0.0.0.1] nssa