From: ALL From_NJ (all.from.nj@gmail.com)
Date: Wed Feb 18 2009 - 00:49:47 ARST
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
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>
-- Andrew Lee Lissitz all.from.nj@gmail.comBlogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sun Mar 01 2009 - 09:44:11 ARST