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Configuring OSPF

Matrix DFE Series and N-SA User’s Guide 8-11

Configuring an OSPF NSSA

Asdescribedin“OSPFAreas”onpage 8‐4,OSPFnetworksaregroupedintoareas.Routing

informationpassedbetweenareasisabstracted,potentiallyallowingasignificantreductionin

routingtraffic.

AnOSPFareacanbeconfiguredas:

•anormalarea(default),whichwouldnotrestrictLinkStateAdvertisements(LSAs),

•astubarea,

whichwouldnotallowLSAsfromexternalroutes,or

•aNotSoStubbyArea(NSSA),whichallowssomeadvertisementsfromexternalroutes.

Whilethestubareareducesthesizeofthelinkstatedatabase(LSDB),NSSAareaconfigurat ion

allowsLSDBreductionwhilestillpermittingtheimportingofselectedexternalroutes.External

routesthatarenotimportedintoanNSSAcanberepresentedbymeansofadefaultroute.This

configurationisusedwhenanOSPFinternetworkisconnectedtomultiplenon‐OSPFrouting

domains.

Procedure 8 ‐2liststhestepsandtheassociatedcommandsnecessarytocompletetheNSSA

configurationprocess.Itassumes

thesametopologyusedinPerformingaBasicOSPF

Configurationonpage 8‐9,onlythisexampleconfiguresarea1asanNSSA,addssecurity

parameters,andestablishesavirtuallinkbetweenarea1andtheOSPFbackbone.

Procedure 8-2 OSPF NSSA Configuration

Step Task Command

1. From switch mode, enter router mode on router 1. router 1

2. Enable router 1. enable

3. Enable global configuration mode. configure terminal

4. Enable interface configuration mode for VLAN 100. interface vlan 100

5. Configure MD5 authentication key 100, and the

associated password “ospfkey” to be used by

neighboring routers.

ip ospf message-digest-key 100

md5 ospfkey

6. Enable router configuration mode for OSPF

instance 1.

router ospf 1

7. Assign network interface 131.108.1.1 to area 1. network 131.108.1.1

255.255.255.0 area 1

8. Configure the area 1 router as an ABR, and set the

scope of the area.

area 1 range 131.108.1.1

255.255.255.0

9. Enable MD5 authentication for area 1. area 1 authentication message-

digest

10. Configure area 1 as an NSSA, allowed to generate

Type 7 LSAs.

area 1 nssa

11. Create a virtual link with MD5 authentication for the

ABR to represent a logical connection between area

1 and the OSPF backbone.

area 1 virtual-link 131.108.1.3

authentication-key 100