From: Scott Morris (swm@emanon.com)
Date: Tue Dec 09 2003 - 10:04:17 GMT-3
The more we go down the path, the more interesting my mental view of
your network becomes. :) This continues to beg questions though.
I assume you are doing an NSSA no summary area for a reason. Why did
you choose the no-summary area over a "regular" nssa area? With NSSA,
you don't get LSA type 4 or 5's into the area from other OSPF places,
and use type 7's within the area. With the no-summary part, you also
don't get LSA type 3's from other OSPF areas. Do you intend to not
reach any of those areas, or do you want to reach all of the other OSPF
areas through R2?
You are correct, that if you have two 0/0 LSAs sent to you, you will
prefer the "internal" type 3 LSA to an "external" type 5 or type 7 LSA.
So make one not happen.
How about your MSFC (I'm assuming this is the one generating the type 3
0/0 LSA), using a distance inter-area 255 to not make the networks that
are typically contained in the type 3 LSAs preferred by anyone when you
do not do the "no summary" part? If you change the distance, then it
doesn't matter whether you do the no-summary portion or not. Unless you
are filtering out of the area as well, you may have asymmetrical routing
going on... Or do you not care about that?
Scott
-----Original Message-----
From: zzk [mailto:ccie_99@yahoo.com]
Sent: Tuesday, December 09, 2003 5:59 AM
To: Brian McGahan; 'Scott Morris'; ccielab@groupstudy.com
Subject: RE: how to filter out default route in OSPF totally stub area?
Hello
Thanks for the illustration, Brian.
Our problem is there is a ABR router R1 generating a
IA type default route into the network (because the
area is totally stub NSSA), and another ASBR R2
generating a external type default route.
All the routers chose R1 as the default gateway,
because LSA type 3 is prefered over LSA type 7.
Is there anyway we can make the routers to select R2
as the default gateway?
There is one ABR LSA type 3 filtering feature, however
it is not avaliable on Cat6 MSFC. :(
thanks
--- Brian McGahan <bmcgahan@internetworkexpert.com>
wrote:
> 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
>
=== message truncated ===
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This archive was generated by hypermail 2.1.4 : Sat Jan 03 2004 - 08:25:38 GMT-3