From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Mon Dec 08 2003 - 17:49:16 GMT-3
A not-so-totally-stubby area (nssa no-summary) is a totally stubby
area that you can redistribute into. The ABR of the NSTSA automatically
originates a default of LSA type-3 into the area:
Rack1R1#sh run | b router ospf
router ospf 1
area 12 nssa
network 12.0.0.1 0.0.0.0 area 12
Rack1R2#sh run | b router ospf
router ospf 1
area 12 nssa no-summary
network 12.0.0.2 0.0.0.0 area 12
network 150.1.2.2 0.0.0.0 area 0
Rack1R1#show ip route ospf
O*IA 0.0.0.0/0 [110/11] via 12.0.0.2, 00:02:49, Ethernet0/0
Rack1R1#show ip ospf database
OSPF Router with ID (150.1.1.1) (Process ID 1)
Router Link States (Area 12)
Link ID ADV Router Age Seq# Checksum Link count
150.1.1.1 150.1.1.1 188 0x80000002 0x0006CE 1
150.1.2.2 150.1.2.2 188 0x80000003 0x00F8D2 1
Net Link States (Area 12)
Link ID ADV Router Age Seq# Checksum
12.0.0.2 150.1.2.2 189 0x80000001 0x001342
Summary Net Link States (Area 12)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 150.1.2.2 211 0x80000001 0x00CBCE
An NSSA for which the ABR originates a default is different (nssa
default-information-originate). This is an LSA type-7 default (N1 or N2, N2
by default):
Rack1R2#sh run | b router ospf
router ospf 1
log-adjacency-changes
area 12 nssa default-information-originate
network 12.0.0.2 0.0.0.0 area 12
network 150.1.2.2 0.0.0.0 area 0
Rack1R1#sh ip route ospf
150.1.0.0/16 is variably subnetted, 3 subnets, 2 masks
O IA 150.1.2.2/32 [110/11] via 12.0.0.2, 00:00:46, Ethernet0/0
O*N2 0.0.0.0/0 [110/1] via 12.0.0.2, 00:00:42, Ethernet0/0
Rack1R1#sh ip ospf database
OSPF Router with ID (150.1.1.1) (Process ID 1)
Router Link States (Area 12)
Link ID ADV Router Age Seq# Checksum Link count
150.1.1.1 150.1.1.1 568 0x80000002 0x0006CE 1
150.1.2.2 150.1.2.2 568 0x80000003 0x00F8D2 1
Net Link States (Area 12)
Link ID ADV Router Age Seq# Checksum
12.0.0.2 150.1.2.2 569 0x80000001 0x001342
Summary Net Link States (Area 12)
Link ID ADV Router Age Seq# Checksum
150.1.2.2 150.1.2.2 54 0x80000001 0x00EF0F
Type-7 AS External Link States (Area 12)
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 150.1.2.2 50 0x80000001 0x0040C7 0
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 708-362-1418 (Outside the US and Canada)
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Scott Morris
> Sent: Monday, December 08, 2003 11:46 AM
> To: 'zzk'; ccielab@groupstudy.com
> Subject: RE: how to filter out default route in OSPF totally stub area?
>
> Well, I'll be damned. Just when you think an RFC makes sense. :)
>
> However, the nssa default-info is the command that must be manually
> done. And when you set up the "no-summary" version, I don't believe
> that automatically generates a 0/0 route, it just prevents other IA
> routes from coming in. So that leaves you with NEEDING to manually
> configure the "nssa default-info" command.
>
> Either way you go there, it still seems to be an administratively
> controlled feature.
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
> CISSP, JNCIS, et al.
> IPExpert CCIE Program Manager
> IPExpert Sr. Technical Instructor
> swm@emanon.com/smorris@ipexpert.net
> http://www.ipexpert.net
>
>
> -----Original Message-----
> From: zzk [mailto:ccie_99@yahoo.com]
> Sent: Monday, December 08, 2003 9:33 AM
> To: swm@emanon.com; ccielab@groupstudy.com
> Subject: RE: how to filter out default route in OSPF totally stub area?
>
>
> Hi Scott
> Thanks for your reply.
> I think there is nssa totally stub areas. You can see
> it at
> http://www.cisco.com/en/US/tech/tk365/tk480/technologies_tech_note09186a
> 0080094a88.shtml#definestub
>
> The exit point of the whole network is inside this
> area 1, so this ASBR has to generate default route for
> the whole network. However we are trying to reduce the
> number of LSAs in this area 1, thats why we also want
> to use totally stub area.
>
> I hope you understand the senario, and appreciate if
> there is any better idea.
>
> regards
> --- Scott Morris <swm@emanon.com> wrote:
> > If your area is "totally stub" then it is NOT
> > "nssa". If it is "nssa",
> > then it is NOT "totally stub". You have to choose
> > one or the other. If
> > you are configuring it as an nssa, then you have to
> > add a specific
> > command to generate a default route, it's not in
> > there automatically.
> >
> > If you are a totally stubby area, it's generated automatically. If
> > you don't want it to do that because there is more than
> > one exit point, then
> > you configured the area wrong.
> >
> > Otherwise, if information is coming from another
> > protocol, you can
> > always play with distance in order to prefer one
> > over the other. But
> > I'd suggest looking to fix your area setup first.
> >
> >
> > Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service
> > Provider) #4713,
> > CISSP, JNCIS, et al.
> > IPExpert CCIE Program Manager
> > IPExpert Sr. Technical Instructor swm@emanon.com/smorris@ipexpert.net
> > http://www.ipexpert.net
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com
> > [mailto:nobody@groupstudy.com] On Behalf Of
> > zzk
> > Sent: Monday, December 08, 2003 5:44 AM
> > To: ccielab@groupstudy.com
> > Subject: how to filter out default route in OSPF
> > totally stub area?
> >
> >
> > Hi
> > We have a totally stubby NSSA configured. Is there a
> > way we can block the default route generated by the
> > ABR?
> >
> > The reason is we need the routers to learn the
> > default
> > from another ASBR instead of this ABR.
> >
> > By default, ABR is automatically injecting a default
> > route of type IA, but ASBR is advertising a default
> > route of external type. Thus all routers chose the
> > ABR
> > instead of this ASBR.
> > Thanks
> >
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