From: Greg Wendel (gwendel@gmail.com)
Date: Wed Feb 18 2009 - 01:53:44 ARST
Here is a great link from Jeff Doyle on OSPF area 0.
http://www.networkworld.com/community/node/19293
On Tue, Feb 17, 2009 at 9:49 PM, ALL From_NJ <all.from.nj@gmail.com> wrote:
> Hello Joe, I hope all is well with you.
>
> My main / first suggestion is for you (and anyone who has yet) to read the
> OSPF design guide. A nice read. Here is a link to it (watch the ugly word
> wrap):
>
>
> http://www.ciscosystems.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml
>
> Area 0 ... hummm ... a lot to say about this. Really too much and too many
> directions to take for this ... but, a quick explanation about what you may
> have seen in your labs, Example lab:
>
> Area 3
> |
> R3 (links in both area 2 and 3)
> |
> Area 2
> |
> R2 (links in both area 2 and 0)
> |
> Area 0
> |
> R1 (area 0 router)
>
> R3 is not connected to area 0, but you still see OSPF routes present when
> you type "show ip route". The short answer is that, inter-area still
> works,
> no magic there. R2 and R3 share an area, area 2, via their links to each
> other, and as such they will share routes.
>
> What does R3 and R1 know about each other? Add some loops on each and see
> who learns what. What happens when the routers exchange routes / DBDs with
> a non-connected area 0 or a discontiguous area 3? What does OSPF do when
> it
> receives an update for an area that it should not be connected to? If it
> should not have gotten an update from a discontiguous router, what should
> it
> do? In short, we configure tunnels and virtual links in order to extend
> area 0 to all.
>
> Would suggest a simple lab test.
>
> From the link above:
> The Backbone and Area 0
>
> OSPF has special restrictions when multiple areas are involved. If more
> than
> one area is configured, one of these areas has be to be area 0. This is
> called the backbone. When designing networks it is good practice to start
> with area 0 and then expand into other areas later on.
>
> The backbone has to be at the center of all other areas, i.e. all areas
> have
> to be physically connected to the backbone. The reasoning behind this is
> that OSPF expects all areas to inject routing information into the backbone
> and in turn the backbone will disseminate that information into other
> areas.
>
> HTH,
>
> Andrew Lee Lissitz
>
>
>
>
> On Tue, Feb 17, 2009 at 5:53 PM, <joe_astorino@comcast.net> wrote:
>
> > Hi guys,
> >
> > I am looking for some clarification regarding OSPF area 0 with respect to
> > what does and what does not have to flow through it as well as how this
> > process works. From what I understand all data packets no longer need to
> > actually go through area 0, but all OSPF routes do need to pass through
> area
> > 0. In other words, in order for non-backbone area routers to exchange
> > routes, they need to first go through area 0. I'm not sure on this
> though.
> > After attempting part of IPexpert volume 3 lab 9, I have much doubt on
> this
> > topic. It seemed like some non-backbone area routers were learning OSPF
> > routes directly from other non-backbone routers. Any clarification on
> this
> > would be much appreciated
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
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>
>
> --
> Andrew Lee Lissitz
> all.from.nj@gmail.com
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>
-- Gregory Wendel Springfield VA, 22153Blogs and organic groups at http://www.ccie.net
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