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Creating a stub area or NSSA

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

A not so stubby area (NSSA) also prevents the flooding of AS-External Link State advertisements into the area by replacing them with a default route. The added feature of NSSAs is the ability to import small stub (non-OSPF) routing domains into OSPF.

To create a stub area or NSSA:

  1. From the Device Manager menu bar, choose IP Routing > OSPF > Areas.
    2. The OSPF dialog box opens with the Areas tab displayed.
  2. Under the ospfImportASExtern field, select the area you want to change to a stub area or NSSA; use the pull-down menu to select importExternal, ImportNoExternal, or importNssa.
  3. Under the ospfImportASExtern field, select the area you want to change to a stub area or NSSA; use the pull-down menu to select importExternal, ImportNoExternal, or importNssa.
  4. Click Apply.

The table below describes the Areas tab fields.


Field Description
Id
A 32-bit integer uniquely identifying an area. Area ID 0.0.0.0 is used for the OSPF backbone.
ospfImportAsExtern
The area's support for importing AS external link state advertisements. Could be importExternal (default), importNotExternal, or importNssa (not so stubby area).
SpfRuns
Used to indicate the number of SPF calculations performed by OSPF.
BdrRtrCount
The total number of area border routers reachable within this area. The value, initially zero, is calculated in each SPF Pass.
ospfAsBdrRtrCount
The total number of Autonomous System border routers reachable within this area. The value, initially zero, is calculated in each SPF Pass.
LsaCount
The total number of link state advertisements in this area's link state database, excluding AS External LSAs.
LsaCksumSum
The 32-bit unsigned sum of the link state advertisements. This sum excludes external (LS type 5) link state advertisements. The sum can be used to determine if there has been a change in a router's link state database and to compare the link state database of two routers.
Summary
The area's support for Summary advertisements in a stub area.
ImportSummary
The area's support for importing Summary advertisements into a stub area. This field should be used only if ospfImportASExtern or importNssa is set to FALSE.
ActiveIfCount
The number of active interfaces in this area.

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