Gareth,
Go directly to the source! RFC 2328, sections 3.1 and 3.2 define area 0 as
the backbone and how traffic flows in a multi-area network, respectively.
Pamela
At 04:53 PM 6/21/01 -0400, you wrote:
>Im fairly sure I understand most of the rules regarding area zero, but have
>heard a few people referring to "the area zero rule". Is there a fixed
>definition of the area zero rule somewhere?
>
>Thanks,
>
>Gaz
>
>""John Neiberger"" wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > In this scenario, with a small number of routers an area zero isn't
> > really necessary. However, expand this to 100 routers in 20 or so
> > groups and an area zero starts to make sense. However, in my original
> > post I wasn't concerned with best practices. I was only curious as to
> > how OSPF would behave if I were to try to configure it that way.
> >
> > I was trying to reconcile a couple of things. I've always read that in
> > multiarea OSPF, all interarea traffic must go through area zero. If
> > areas are defined by links and not routers, then does that mean all
> > traffic must flow over a link defined as area zero? That was really the
> > issue and Pamela answered that for me.
> >
> > This scenario occurred to me while reading the area zero rule and then
> > thinking about a hub-and-spoke configuration with a single hub router.
> > I would never suggest that someone actually configure the network that
> > way, I simply was wondering how OSPF would behave in a hub and spoke
> > network with no area zero configured. As it turns out, the loopback
> > interface can be placed in area zero, thus fulfilling that requirement.
> >
> > John
> >
> > >>> "Chuck Larrieu" 6/21/01 10:28:12 AM >>>
> > A couple of questions / thoughts
> >
> > In the scenario mentioned, is an area zero really necessary? I.e. why
> > not
> > throw all routers into a singe area, whatever it's name? In hub and
> > spoke,
> > all inter-spoke traffic will have to go through the hub anyway, no
> > matter
> > what the protocol.
> >
> > Another thing to keep in mind, is that OSPF does not in and of itself
> > change
> > the way routing works. When a router receives a packet, it checks the
> > destination address, compares this to routes in the routing table, and
> > if
> > there is a match, forwards the packet out the appropriate interface. It
> > does
> > not say "hmmm, I have a directly connected interface that matches, but
> > this
> > is an OSPF router, therefore I will forward the packet to the backbone
> > router first" :->
> >
> > How's stuff, Pamela?
> >
> > Chuck
> >
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf
> > Of
> > Pamela Forsyth
> > Sent: Thursday, June 21, 2001 9:09 AM
> > To: [EMAIL PROTECTED]
> > Subject: Re: OSPF Hub and Spoke [7:9268]
> >
> > John,
> >
> > I just tried this out, and the newer IOS versions (after 11.2) *will*
> > let
> > you use a loopback interface as area 0 with different non-zero areas
> > defined on the spokes.
> >
> > There is no reason for the traffic actually to travel over the area 0
> > link,
> > but area 0 must be in the hub router for the inter-area LSAs to be
> > advertised to the spoke routers. OSPF is just populating the IP
> > routing
> > table; it is not making forwarding decisions. The router in this
> > instance
> > will not try to send traffic over an extra link just because of an
> > OSPF
> > rule about backbones. ;-)
> >
> > Again, your mileage may vary, depending on IOS version.
> >
> > Pamela
> >
> > At 09:54 AM 6/21/01 -0400, you wrote:
> > >Yes, I'm replying to myself.
> > >
> > >While doing some reading it occurred to me why *not* extending area 0
> > across
> > >the WAN links should not work. In OSPF, unlike IS-IS, an area is
> > defined
> > by
> > >links, not routers. The rule states that interarea traffic must go
> > through
> > >area 0. Well, if areas are defined by links, then this means that
> > interarea
> > >traffic must at least go across one link that is defined as an area 0
> > link.
> > >
> > >In a hub-and-spoke environment with a single hub router, it seems to
> > me
> > that
> > >there just is no good way to use multiarea OSPF if you don't extend
> > area 0
> > >across the WAN links.
> > >
> > >At least, that's the way it appears at the moment.
> > >
> > >John
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=9431&t=9268
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