[nsp] OSPF Area Design

David Curran dm at nuvox.net
Wed Feb 25 22:56:35 EST 2004

Is it too simplistic to say that with only 10 routers in your network and
not much chance for flap that all routers would be in Area 0?  I realize it
makes a pretty picture on a whiteboard to make each router its own area but
I'm not sure its necessary.  For example:

1.)  Each office with 'Net access has a static route to ISP pointed to the
1A.) Above router advertises default route as metric-type 1 using:
     'default-information originate metric-type 1'

2.)  Manually configure costs on each routers subinterface to reflect your
preference.  e.g. A Chicago to LA link is 'ip ospf cost 10000' and a Chicago
to St. Louis link would be 'ip ospf cost 5000'.

Its as simple as it gets.  2 lines under the ospf processes (ok, 3 if you
add no auto-cost) and 1 under the interface.  If there's chance for any real
growth (i.e. 20 or 30 routers in area 0) then maybe you should break it into
areas.  However, most stable (read 'no dial-up') networks can grow very
large in one area with no problems.

Just a thought ;-)

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Vandy Hamidi
Sent: Wednesday, February 25, 2004 5:15 PM
To: cisco-nsp at puck.nether.net
Subject: [nsp] OSPF Area Design

Current State:
 -4 Remote offices
	-3 have dedicated Internet
 -1 Main Office
	-Offices fully meshed through Frame-Relay
	-Has dedicated INet
 -2 Remote Data Centers
	-Data Centers fully meshed with Main office

We're Configuring OSPF for our 4 remote and Main offices using Frame-Relay
to fully mesh all locations.
Our main office also has a fully meshed point-to-point network with our 2
data centers.
We'll have 4 connections to the internet from our 5 offices and we'd like to
be able to provide (originate 0/0) internet access to all offices (current
and new) as a backup for those that have dedicated Inet and primary for
offices w/o dedicated Inet.

All offices need to communicate directly with each other over the WAN.

We're currently using Static routes, but want to move to dynamic routing for
resiliency and ease of scalability.  We chose OSPF because it's compatible
with our Cisco and non-Cisco equipment.

What's the best way to design the OSPF Areas that will give us the most
effective routing and resiliency to failures while still maintaining a
simple configuration?


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