nssa (OSPF area view)

Function

The nssa command configures an NSSA.

The undo nssa command cancels the configuration of an NSSA.

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

Format

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 ] ^*

undo nssa

Parameters

Parameter	Description	Value
default-route-advertise	Generates default Type 7 LSAs on the ABRs or ASBRs and then advertises them to the NSSA. The ABR automatically generates default Type 7 LSAs and advertises them to the NSSA only when at least a neighbor in Full status and an interface that is Up exist in the backbone area.	-
backbone-peer-ignore	Prevents 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.	-
no-import-route	Indicates that no external route is imported to an NSSA.	-
no-summary	Indicates that an ABR is prevented from sending summary LSAs to the NSSA.	-
set-n-bit	Sets the N-bit in DD packets.	-
suppress-forwarding-address	Sets the FA of the Type 5 LSAs translated from Type 7 LSAs to 0.0.0.0 by the NSSA ABR.	-
translator-always	Indicates an ABR in an NSSA as an all-the-time 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.
zero-address-forwarding	Sets the FA of the generated NSSA LSAs to 0.0.0.0 when external routes are imported by the ABR in an NSSA.	-

Views

OSPF area view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ospf	write

Usage Guidelines

Usage Scenario

If you need to import AS external routes to an area and prevent these routes from consuming resources, you can configure the area as an NSSA. The NSSA imports AS external routes and transmits them to the entire OSPF AS.

All devices in an NSSA must be configured with NSSA attributes using the nssa command. Parameters of the nssa command are used as follows:

Default Type 7 LSAs are generated and advertised to an NSSA when the following conditions are met:

Neighbors in the Full state and interfaces in the Up state must exist in the backbone area.
The default-route-advertise parameter is configured.
The route 0.0.0.0 exists in the local routing table. (If the vpn-instance-capability simple command is configured for a private network, the default-route-advertise command must be configured, and a default route exists in the local routing table.)
The OSPF process is bound to a VPN instance.
If condition 1 is met, ABRs generate default Type 7 LSAs and advertise them to the NSSA. If conditions 2 and 3 are met, the ASBR can generate default Type 7 LSAs and advertise them to the NSSA.

If an ASBR also functions as an ABR, set the no-import-route parameter to prevent 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 the parameter no-summary on an ABR. This prevents 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 that is Up exists in the backbone area. The default Type 3 LSAs preferentially take effect.
After set-n-bit is configured, the N-bit is set in the DD packets during the synchronization between the local and neighboring devices.
If multiple ABRs are deployed in an NSSA, the system automatically selects an ABR (generally the with the largest router ID) as a translator to translate Type 7 LSAs into Type 5 LSAs. You can also configure translator-always on an ABR to specify the ABR as a translator. If you configure translator-always on two ABRs, they both function as translators and implement load balancing. The value of interval-value must be greater than the flooding interval.The suppress-forwarding-address is used to disable translated Type 5 LSA from inheriting the forwarding addresses of FA.
The translator-interval parameter is used to ensure smooth switching of translators. The value of translator-interval must be greater than the flooding period.

Configuration Impact

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

Set a loopback address for the Router in the NSSA so that the loopback address can be automatically selected as the FA. If other Routers have routes of the same cost to the Router in the NSSA, load balancing is performed.

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 Router in the area will be deleted immediately. The local Router still reserves useless Type 5 LSAs received from other Routers. 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] ospf 1
[*HUAWEI-ospf-1] area 1
[*HUAWEI-ospf-1-area-0.0.0.1] nssa