From: James MacDonald (j4m3sm63@yahoo.ca)
Date: Fri Oct 19 2007 - 07:01:12 ART
I think i'm piecing this together then ... There are certain concepts we do
in practice with protocols like OSPF that in a lot of cases are done because
we've been doing it for 12-13 years ... but never truly understood "why" we
had to do it that way. I'm sure there are still several of those issues out
there for me ... I appreciate the assistance.
Thanks
------------------------------
Jim MacDonald
j4m3sm63@yahoo.ca
------------------------------
----- Original Message ----
From: Scott Morris
<smorris@ipexpert.com>
To: James MacDonald <j4m3sm63@yahoo.ca>;
ccielab@groupstudy.com
Sent: Friday, October 19, 2007 12:04:36 AM
Subject: RE:
OSPF - area design question
DIV {
MARGIN:0px;}
According to your
drawing though, that meant that the
method a packet would use to cross one
place or another could not traverse
from/to every single link within Area 1
alone. That constitutes a
discontiguous area.
If you had made one of the
sides an area 2, I think things
would have been fine.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical
Training -
IPexpert, Inc.
IPexpert Sr.
Technical Instructor
A Cisco Learning
Partner - We Accept Learning Credits!
Telephone:
+1.810.326.1444
Fax:
+1.810.454.0130
http://www.ipexpert.com
From:
James MacDonald [mailto:j4m3sm63@yahoo.ca]
Sent: Thursday, October 18, 2007
10:27 PM
To:
smorris@ipexpert.com; ccielab@groupstudy.com
Subject: Re: OSPF -
area
design question
I
think what I was looking for was an idea of what
constitutes a discontigous
area. In my example I had a regular router in
area1 only ... connected with 2
PTP links back to 2 separate ABRs ... each
link a different cost. The ABRs were
connected together with only a single
link in area0 ... in my lab routing was
not working properly. I.e. ABR1 saw
paths to the area router via it's link at
cost 40 and ABR2 only saw it's own
path to the area router at the cost of 80
(those were my set costs) ... it
should see the path via ABR1 as better but it
wasn't.
When i enabled a new
link between the ABR's in area1 then it
worked properly.
Hope this makes
sense the way i describe ... i'm a bit
burnt out at the moment :)
Thanks
------------------------------
Jim
MacDonald
j4m3sm63@yahoo.ca
------------------------------
-----
Original Message ----
From: Scott
Morris <smorris@ipexpert.com>
To:
James MacDonald <j4m3sm63@yahoo.ca>;
ccielab@groupstudy.com
Sent:
Thursday, October 18, 2007 9:58:21 PM
Subject:
RE: OSPF - area design
question
Per your other e-mail, I don't think it has
anything to do with
a "worthy"
question or not, just that ASCII art is scary.
:)
In
any event, I'm not sure what your basic question here actually is.
If
you are looking as to whether this is a valid network design or not,
the
short answer is no. Per OSPF RFC, everyone inside an area must have
an
identical database for that area. Having ANY discontiguous area
screws that
up.
We can fix that with tunnels or virtual links, but
that doesn't make it
a
good idea!
The whole point of an area is an
addressing hierarchy, which
theorhetically
gives us the ability to
aggregate/summarize our routes for
more efficient
routing. If you start
band-aiding things together, you'll
slowly degrade
that idea to where it just
plain doesn't work.
HTH,
Scott
Morris, CCIE4
(R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153,
JNCIS-ER,
CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training -
IPexpert,
Inc.
IPexpert Sr. Technical Instructor
A Cisco Learning Partner -
We
Accept Learning Credits!
Telephone:
+1.810.326.1444
Fax: +1.810.454.0130
http://www.ipexpert.com
-----Original
Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf
Of
James MacDonald
Sent: Monday, October 15, 2007 10:05 PM
To:
ccielab@groupstudy.com
Subject:
OSPF - area design question
In an
environment with 2 core routers in ospf
area 0 connected back-to-back
... and
a distribution router in a separate
area connected to both cores
with PTP
links ... do i need another link
between the cores within the same
regional
area for continuity of the area???
The ASCII art version of the
network would
be like this:
_area1_ RTR1 _area1_
/
\
/
\
C1 ----- area 0 ------
C2
so do I need this?
_area1_ RTR1
_area1_
/
\
/
\
C1 \ -----
area 0 -----
/
C2
\----- area 1 ------/
Hope
this makes sense ...
my formatting may mess up in email ...
Thanks,
------------------------------
Jim MacDonald
j4m3sm63@yahoo.ca
------------------------------
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