I don't know about the genius part. >:-) But, you've described the
initial scenario I was asking about. In my original post I wasn't
suggesting that this would be a good design by any means. I simply was
wondering if it was possible and how you'd configure it.
In this particular case, the hub router is participating in 20 areas
which would cause it to be very busy, especially if the network wasn't
very stable. It would be better to extend area zero across the WAN
links to insulate the hub router from any instability in the outlying
areas.
John
>>> "Stephen Skinner" 6/22/01 4:50:10 AM >>>
Guys,
lets see how my ospf is going ......
in this design goal i would have thought you would have done this ....
hub and spoke....at the hub you have say 1 router (3620) with one
interface
and 20 sub-interfaces.......
you also have 20 totally stubby area`s which connect into the hub...
config each stub as area 1 through 20
setup each sub int as per area`s 1-20
then setup the lan int as area 0
this way you have one router (hub) which is in area 0 and all the
other
area`s aswell........
problem solved ????..
something tells me i`ve just either
A got it right and am a genius
B completely missed the point and broken every rule of ospf
YOU DECIDE
steve
>From: "Chuck Larrieu"
>Reply-To: "Chuck Larrieu"
>To: [EMAIL PROTECTED]
>Subject: RE: OSPF Hub and Spoke [7:9268]
>Date: Fri, 22 Jun 2001 01:15:31 -0400
>
>John, this one's got me to thinking a little bit. Your kinda right but
>kinda
>wrong.
>
>The areas are an OSPF structure, used for the building of the SPF
tables.
>It's not that inter area traffic has to go through a discreet area 0,
but
>that in OSPF in order for an area to learn about routes to another
area
>there has to be an area 0 router in between them. It does not matter
if
>there are a number of interfaces that are ABR's, or if there is a
discrete
>and pure area 0.
>
>With OSPF, all that matters is that the appropriate adjacencies are
formed,
>and that the LSA's are processed and that the OSPF database is
created. If
>all that occurs, OSPF routes will be placed into the routing tables.
As far
>as the router itself is concerned, routing is independent of the
routing
>protocols involved.
>
>I've fooled with this in the past. I'll have to do another Q&D lab to
>gather
>some evidence, and post it here over the weekend.
>
>In the meantime, for those interested in some in-depth discussion of
>routing, Howard's white paper on Certification Zone is definitely
worth
>reading. I have not seen the likes of it in any other source,
including
>Doyle ( although it has been too long since I've read Doyle )
>
>Chuck
>
>
>-----Original Message-----
>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf
Of
>John
>Neiberger
>Sent: Thursday, June 21, 2001 6:55 AM
>To: [EMAIL PROTECTED]
>Subject: Re: OSPF Hub and Spoke [7:9268]
>
>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
>
>| I'm having trouble wrapping my brain around a specific scenario and
I
>| wanted to get your thoughts. Let's say we have a hub and spoke
network
>| with a single router as the hub. There are five areas attached to
the
>| backbone. It seems that we would have to extend area 0 across the
WAN
>| links, but I'm wondering what would happen if we didn't.
>|
>| If we didn't, the backbone router would have no interfaces in area
0.
>| I'm wondering if this would cause some major problems. I bet that
it
>| would but I'm having a hard time thinking through what actual
problems
>| might arise. Would this backbone router just "know" that it was
area 0
>| because it has interfaces in multiple non-zero areas and hence
behave
>| correctly?
>|
>| One obvious problem is that the backbone router would be a member
of
>| every area and would thus be pretty busy if the network got to be
very
>| big. If we extended area 0 across the WAN link the backbone
router
>| would be protected from running SPF calculations everytime a remote
area
>| had a link change.
>|
>| What other problems would arise? Would this even work at all? I
don't
>| really have the tools to try it or I'd just attempt this chaos
myself.
>| As you can guess, we run eigrp everywhere so I'm still clueless to
some
>| of the workings of OSPF in a production environment.
>|
>| Regards,
>| John
>|
>|
>|
>|
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