Creating an OSPF area

Create an area to subdivide the autonomous system (AS) into areas that group contiguous networks, routers that connect to these networks, and attached hosts. Subdividing the AS into areas significantly reduces the amount of routing protocol traffic compared to treating the entire AS like a single link-state domain.

About this task

A stub area does not receive advertisements for external routes, which reduces the size of the link-state database (LSDB). A stub area uses only one area border router (ABR). Any packets destined for outside the area are routed to the area border exit point, examined by the ABR, and forwarded to a destination.

A not so stubby area (NSSA) prevents the flooding of AS-External link-state advertisements into the area by replacing them with a default route. NSSAs also import small stub (non- OSPF) routing domains into OSPF.

Before you begin

You configure OSPF on a VRF instance the same way you configure the GlobalRouter, except that you must use VRF Router configuration mode and replace ipv6 with ipv6 ospf.

Procedure

Enter OSPF Router Configuration mode:

enable

configure terminal

router ospf
Specify the area ID:

ipv6 area {A.B.C.D}
Configure optional area parameters if the default values do not meet your requirements:
1. Configure the area type if you need a stub or NSSA area:
  
  ipv6 area {A.B.C.D} type <nssa|stub>
  
  By default, the area is a normal area; neither a stub nor NSSA area.
2. Configure the default cost:
  
  ipv6 area {A.B.C.D} default-cost <0-16777215>
  
  You do not need to configure this parameter if the area is a normal area.
3. Configure the area support for importing advertisements:
  
  ipv6 area {A.B.C.D} import <external|noexternal|nssa>
  
  The default is external.
4. Disable the importation of summary advertisements into a stub area:
  
  no ipv6 area {A.B.C.D} import-summaries enable
  
  The default is enabled.
5. Configure translation of Type 7 LSAs into Type 5 LSAs:
  
  ipv6 area {A.B.C.D} translator-role <1–2>
  
  The default value is 2–candidate.

Example

Specify the area ID:

Switch:1(config-ospf)#ipv6 area 0.0.0.1

Variable definitions

Use the data in the following table to use the ipv6 area command.


Variable	Value
{A.B.C.D}	Specifies a 32–bit integer to uniquely identify an area. Use 0.0.0.0 for the OSPFv3 backbone.
default-cost `<0-16777215>`	Configures the metric value advertised for the default route to stub and NSSA areas.
import <external\|noexternal\|nssa>	Configures area support for importing AS-external LSAs: external—normal area noexternal—stub area nssa—not-so-stubby area AS-scope LSAs are not imported into stub areas or NSSAs. NSSAs import AS-External data at Type 7 LSAs, which use area scope. The default is external.
import-summaries enable	Controls the import of inter-area LSAs into a stub area. If you disable this parameter, the router does not originate nor propagate inter-area LSAs into the stub area. If you enable this parameter (the default), the router both summarizes and propagates inter-area LSAs.
<nssa\|stub>	Configures the type of area. By default, the area is neither a stub area or an NSSA.
translator-role `<1–2>`	Indicates if the NSSA border router can perform NSSA translation of Type 7 LSAs to Type 6 LSAs. The possible values are always (1) or candidate (2). The default is candidate (2).