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Re: OSPF to Internet Q [7:61823] posted 01/25/2003
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Steve Ringley wrote:
> That is why I am asking the question - it is unclear!  Let me
> try it this
> way:
> If we take the textbook Internet setup, we would have an
> outside router - BGP
> firewall
> inside router - OSPF ASBR to BGP
> core router - OSPF backbone
> On the inside router, would I create an ASBR with area 0
> defined on the
> inside to core connection
> or
> Would I create an new OSPF area to define the connection
> between the inside
> router and the core router?

I think you could do either one. Your core router connects (downwards in
your picture) to Area 0 (the OSPF backbone), right?

So, does your question boil down to whether the link between the inside
router and the core router should be in Area 0 or a new Area? I think you
could do it either way.

> There are several of these types of connections in the larger
> network, and
> there is an expectation that if one of these goes down the OSPF
> and BGP will
> figure it out and shift traffic to the working connections.

OSPF should figure out which routes to the ASBRs are up. Your inside routers
should inject an ASBR Summary LSA into Area 0 to make sure other routers
know about the routes to the ASBRs.

I don't think BGP is involved at this point. It sounds like you just run
that to the outside world.

You'll need to consider how traffic gets back in to.

So, this is large-scale design, I'm realizing. You need more help than I can
give! :-) Maybe Peter, Howard, Chuck, etc. could pipe in, or maybe do some
paid consulting work for you!?


> ""Priscilla Oppenheimer""  wrote in
> message
> news:200301250118.BAA24614@xxxxxxxxxxxxxxxxx
> I'm afraid your question isn't clear.
> By definition, an ASBR connects two unlike networks, one that
> is running
> OSPF and one that isn't. So, the ASBR will connect to the
> Internet in your
> example.
> Steve Ringley wrote:
> >
> > I have an OSPF network, and I have my Internet connections. 
> Do
> > I:
> >
> > ASBR where traffic goes from area 0 to the Internet
> Is that where your Internet connection is? In area 0? Often, it
> is, and
> that's where your ASBR will be.
> >
> > or
> >
> > ASBR where traffic goes to an area x then to the Internet?
> Goes from where to an Area x and then to the Internet?? This is
> where your
> question gets unclear. But if you are considering putting an
> ASBR between
> Area x and Area 0, then that doesn't make sense. It's not an
> ASBR because
> it's connecting two OSPF networks. If your Internet connection
> is in Area X,
> you will have an ASBR that connects the OSPF world to the
> Internet, sitting
> on the edge of Area X.
> Are you asking if the ASBR should be in Area 0? I think the
> answer is yes,
> if it can, but sometimes that's simply not possible on large
> internetworks
> with multiple egress points.
> If I completely missed what you're getting at, sorry!
> Priscilla
> >
> > This was never clear to me from my reading.

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