>>> SNIP
Here's a slightly different question though for
anyone. Could an ABR
that
is connected to a stub area (not an NSSA area) be an
ASBR? In other
words,
does the fact that the router is a backbone router and
possibly
connected
to other areas as well make it exempt from the rule
that you can have
no
ASBRs in a stub area? In this situation would the
router just not
advertise it's type 4 and 5 LSAs into that particular
area?
>>> END SNIP
Curtis, I set up a lab config along the following
lines:
Router 1 had eth 0 in Area 0.
Router 1 had s0 in area 1.
I redistributed RIP into OSPF and vice-versa.
Thus Router 1 was ABR/ASBR.
I the tried to make area 1 a stub area and an error
was generated 'cannot have ASBR in a stub area'
HTH,
I didn't keep the configs for that one, but I'll
reproduce if you like ?
Phil.
--- Curtis Call <[EMAIL PROTECTED]> wrote: > That's
kindof the conclusion I have come across too,
> that OSPF just isn't
> designed to be able to do this selectively.
> Obviously blocking LSA type
> 1's or 2's within an area would directly violate the
> RFC since ever
> Router's link state database in a certain area has
> to match, and given that
> you redistribute into the OSPF process itself and
> not into a given area it
> makes sense that barring certain exceptions such as
> stub areas an ASBR will
> always send the LSA 5's into every connected area.
> Here's a slightly different question though for
> anyone. Could an ABR that
> is connected to a stub area (not an NSSA area) be an
> ASBR? In other words,
> does the fact that the router is a backbone router
> and possibly connected
> to other areas as well make it exempt from the rule
> that you can have no
> ASBRs in a stub area? In this situation would the
> router just not
> advertise it's type 4 and 5 LSAs into that
> particular area?
>
> At 11:52 AM 2/2/01 -0500, you wrote:
> >So you are talking about a topology where you have
> an ASBR that also
> >borders Area 0 and is thus also an ABR by
> definition.
> >
> >The question is then, "can I control which external
> prefixes enter the
> >rest of the ospf domain as type 5 LSA's" I would
> have to say that you
> >cannot by definition restrict the flow of LSA's in
> an OSPF domain beyond
> >turning down interfaces. You can decide which
> area's will recieve Type
> >3/4/5/7/10 etc by the use of stub areas and their
> variants and you can
> >also minimize prefix flow's by summarizing at
> borders. However, there is
> >no way to my knowledge that you can instruct a ABR
> to advertise some but
> >not all type 5's into an area.
> >
> >Route filtering in OSPF is somewhat of a misnomer
> in my opinion. Since
> >link state protocols do not advertise their routing
> table, but instead
> >their link state database, the concept of prefix
> filtering within an OSPF
> >domain is out of place. In fact, filting LSA's of
> any kind within an area
> >directly violates the RFC in that all routers in an
> Area MUST maintain
> >identical copies of the area topology. However,
> filtering type 5's at the
> >ABR, to me, has some merits. I may be missing
> something here and Howard
> >will likely point it out if I am. But in summary,
> there is no
> >"distribute-list" type command that allows you to
> restrict the flow of
> >LSA's within an OSPF domain.
> >
> >Naturally I'm sure your aware that you can filter
> prefixes like mad when
> >dealing with redistribution into or out of OSPF.
> >
> >HTH
> >
> >-pete
> >
> >
> >*********** REPLY SEPARATOR ***********
> >
> >On 2/2/2001 at 7:48 AM Curtis Call wrote:
> >
> > >Anything, but to make it simple lets just say
> we're trying to redistribute
> > >static routes.
> > >
> > >At 08:41 AM 2/2/01 -0500, you wrote:
> > >>Redistribute what?
> > >>
> > >>
> > >>*********** REPLY SEPARATOR ***********
> > >>
> > >>On 2/1/2001 at 8:02 PM Curtis Call wrote:
> > >>
> > >> >There's something that I'm curious about
> dealing with OSPF ASBRs. Let's
> > >> >say your ASBR is also an ABR that is bordering
> area 0 and area 1. Is
> > there
> > >> >a way that you could specify to only
> redistribute into area 1 or by
> > nature
> > >> >of being an ASBR does a router have to
> advertise the route to every
> > area to
> > >> >which it is connected (assuming all areas are
> normal non-stub areas).
> > >> >
> > >> >_________________________________
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