From: John Underhill (stepnwlf@magma.ca)
Date: Mon Dec 08 2003 - 14:12:32 GMT-3
In that scenario, I put the distance command on the ABR generating the route,
at which point all NSSA routers in the area lose the default route. If you
wanted to advertise the default route from the ASBR at the point of
redistribution, rather then the ABR, I would create the default route in the
other protocol and let OSPF get the route from redistribution.
AREA 0 -- R1 -- AREA 1 NSSA/NS -- R2 -- RIP-- R4
Before distance command was applied, default route was generated by the ABR,
as seen in the routing table on R2:
C 202.1.1.0/24 is directly connected, Loopback0
150.50.0.0/24 is subnetted, 3 subnets
C 150.50.1.0 is directly connected, Serial1
C 150.50.9.0 is directly connected, Dialer0
C 150.50.17.0 is directly connected, Ethernet0
O*IA 0.0.0.0/0 [110/65] via 150.50.1.1, 00:13:17, Serial1 <default route
generated by ABR/>
If you want to generate the default route from the ASBR, simply create the
default route in the other protocol domain, and redistribute it into OSPF at
the ABR.
R 204.1.1.0/24 [120/1] via 12.1.1.4, 00:00:10, Serial0
C 202.1.1.0/24 is directly connected, Loopback0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0
150.50.0.0/24 is subnetted, 2 subnets
C 150.50.1.0 is directly connected, Serial1
C 150.50.17.0 is directly connected, Ethernet0
R* 0.0.0.0/0 [120/12] via 12.1.1.4, 00:00:10, Serial0
The distance command simply invalidates the single type 3 LSA injected into
the area by the ABR. Try running debugs and then adding the distance command
to see the LSA state change in action.
----- Original Message -----
From: zzk
To: John Underhill ; swm@emanon.com ; ccielab@groupstudy.com
Sent: Monday, December 08, 2003 10:35 AM
Subject: Re: how to filter out default route in OSPF totally stub area?
Thanks, John
This is a smart idea.
Got one more question (Just to help me to understand
it better). I thought the distance 255 method will
block the route to be inserted into the particular
router's routing table, does it affect the LSA sent
out or does it affect how the rest of routers build
their routing table?
regards
--- John Underhill <stepnwlf@magma.ca> wrote:
> On the border router simply apply distance of 255
> and route will be removed from NSSA routers..
>
> router ospf 100
> area 1 nssa no-summary
> passive-interface default
> no passive-interface Serial0
> network 150.50.1.0 0.0.0.255 area 1
> network 201.1.1.0 0.0.0.255 area 0
> distance 255 0.0.0.1 255.255.255.0 1
> !
> access-list 1 permit 0.0.0.0
> ----- Original Message -----
> From: zzk
> To: swm@emanon.com ; ccielab@groupstudy.com
> Sent: Monday, December 08, 2003 9:33 AM
> 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_note09186a008
0094a88.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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